adult ticket cost 3 times as child, they spend 36.00, how much is child ticket
adult ticket = 3 * child ticket
adult + child = 36
substitute in:
3 child ticket + child ticket = 36
4 child ticket = 36
child ticket = 9
adult + child = 36
substitute in:
3 child ticket + child ticket = 36
4 child ticket = 36
child ticket = 9