If 2 adult tickets and 1 child ticket cost $8 and if 1 adult ticket and 3 child tickets cost $9, what is the price of each ticket

Answer 1

2A + C = 8

A + 3C = 9

Multiply second equation by 2.

2A + 6C = 18

Subtract first equation from revised second.

5C = 10

Work it from there.

Answer 2

2a + c = 8
a + 3c = 9

I suggest substitution, from #1, let c = 8-2a
plug into #2