Answer :
adult= a, kids under 12 = k
[cost of tickets] 4.50a + 2k = 330 ---(1)
[number of tickets] a+k = 90 ---(2)
(2) multiplied by 2
so 2a + 2k = 180 ---(3)
(1) minus (3)
so 2.50a = 150
a = 60
then a+k = 90
60+k = 90
so k = 30
Then 60 adult tickets and 30 kids under 12 were sold.
[cost of tickets] 4.50a + 2k = 330 ---(1)
[number of tickets] a+k = 90 ---(2)
(2) multiplied by 2
so 2a + 2k = 180 ---(3)
(1) minus (3)
so 2.50a = 150
a = 60
then a+k = 90
60+k = 90
so k = 30
Then 60 adult tickets and 30 kids under 12 were sold.