Question

At a school play, children’s tickets cost $3 each and adult tickets cost $7 each. The total amount of money earned from ticket sales equals $210. Which is the number of children's tickets sold for the school play?

Answer 1

Your question is incompatible to find any exact answer

210 = 7a + 3c
210 - 7a = 3c
(210 - 7a)/3= c

now graph it as
y = (210-7x)/3

Answer 2

It's 70. Cause 3 × 70 is 210.