For a saturday matinee, adult tickets cost $4.50 and kids under 12 pay only $2.00. if 90 tickets are sold for a total of $330, how many of the tickets were adult tickets and how many were sold to kids under 12

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.