android - How to time an activity out after a certain timeframe? -

i want create application in user has 90 seconds in order complete number of sums.

i unsure how stop activity , move after timeframe up?

activity code:

/**  * class holding activity has 10 random sums user answer  * @author ross  *   */ public class randomtest extends activity implements view.onclicklistener {     // declare vars     textview text;     edittext answer;     button submit;     int random1;     int random2;     string[] question = new string[10];     int correctanswer[] = new int[10];     int[] results = new int[10];     int score = 0;     int questionnumber = 1;     mediaplayer correctnoise;     mediaplayer incorrectnoise;     imageview imagerandom;       @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);          setcontentview(r.layout.test);          // initialising variables         initialisevars();          // set random         setuprandom();          // set text view equal question in array         text.settext(question[questionnumber - 1]);          // set on click listener submit button         submit.setonclicklistener(this);          // updatequestion         updatequestion();      }      /**      * method initialises variables      */     public void initialisevars() {          correctnoise = mediaplayer.create(randomtest.this, r.raw.correctnoise);         incorrectnoise = mediaplayer.create(randomtest.this, r.raw.incorrectnoise);         text = (textview) findviewbyid(r.id.tvtoprandomtest);         answer = (edittext) findviewbyid(r.id.etenteranswerrandomtest);         submit = (button) findviewbyid(r.id.btnsubmitrandomtest);         imagerandom= (imageview) findviewbyid(r.id.imageviewrandomtest);      }      /**      * method creates random sum user answer      */     public void setuprandom() {          // setting new random         random random = new random();          // generating random number between 1 , 12         random1 = random.nextint(12) + 1;         // generating random number between 1 , 12         random2 = random.nextint(12) + 1;         // creating random question string         question[questionnumber - 1] = random1 + " x " + random2 + " = ";         // creating correct answer question         correctanswer[questionnumber - 1] = random1 * random2;       }      /**      * method updates question after each click      */     public void updatequestion() {          // updating question after each click         setuprandom();         text.settext(question[questionnumber - 1]);         answer.settext("");      }      public void onclick(view v) {          // sets text view equal entered in edittext         final string entry = answer.gettext().tostring();         // convert string value int         int = integer.parseint(entry); //          // setting user answer equal correct part of results array         results[questionnumber - 1] = a;          // if user answer equal correct answer increase score         if (a == correctanswer[questionnumber - 1]) {             score++;             correctnoise.start();             imagerandom.setimageresource(r.drawable.thumbsup);         }else{              incorrectnoise.start();             imagerandom.setimageresource(r.drawable.thumbsdown);          }          // if question number under 10         if (questionnumber < 10) {             // updates question number             questionnumber++;             // called after answer given             updatequestion();          } else {              // passing values results activity             intent intent = new intent(this, randomtestresults.class);             intent.putextra("results", results);             intent.putextra("questions", question);             intent.putextra("correctanswer", correctanswer);             intent.putextra("score", score);             // start activity             this.startactivity(intent);          }      } 

}

use alarmmanager , when calls use finish();