Tickets for a school play cost $4 for adults and $2 per students. at the endof the play, the school sold 105 tickets and collected $360.
-write a linear system that models the situation.
-find the number of adult and students tickets sold.

First set your variables: let x be the number of adult tickets and let y be the number of student tickets. Now when you write 4x it will say how much money came from adult tickets, and 2y will do the same for students. 4x+2y= the amount of money collected.
4x+2y=360
Solve the above equation for x and y and that will give you the number of tickets sold.

4x+2y=360
x+y=  105 => 4x+4y= 4*105= 420
                    4x+2y =360

                    4y-2y = 420-360= 60
                     2y   = 60    => y= 60:2=30 => x= 105-30=75
Verify 4*75+2*30= 300 + 60 = 360

These are the multiples of 15 but what you are probably asking or what are the factors of 15