Please help me, when saying the answer please say why it is and show your work

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

2y= 3 2 x−2 y = − 1 3 x + 1 y=− 3 1 x+1

65% of students in your school participate in at least one after school activity. if there are 980 students in you school, how many do not participate in an after school activity?