We are given :
The cost of one adult ticket = a.
The cost of one child ticket = c.
Roy buys
6 adult tickets and 2 child tickets.
Total amount = $66.
Therefore, first equation for Roy total amount would be
6a +2c = 66 --------------------(1)
Elisa buys
5 adult tickets and 4 child tickets.
Total amount = $62.
Therefore, second equation for Elisa total amount would be
5a +4c = 62 --------------------(1).
Therefore,
Roy 6a + 2c = 66
Elisa 5a + 4c = 62.