Hello!
Let 'a' stand for adult tickets and 'c' for children tickets.
a + c = 15
(Both adult and children tickets make up a total of 15 tickets).
30a + 20c = 330
a = 3
c = 12
A N S W E R:
William bought 3 adults tickets and 12 children's tickets.
5y-30=-5y+30
add 30 to both sides
5y = -5y+60
add 5y to both sides
10y = 60
divide both sides by 10
y = 6
<em>hope this helps!</em>