assigning "a" as cost of adult tickets and "c" the cost of children's tickets.
3a + 4c = 107
2a + 3c = 76
elimination method
2(3a + 4c = 107)
-3(2a + 3c = 76)
6a + 8c = 214
-6a - 9c = -228
----------------------
0 - c = - 14
c = 14
Then 2a + 3(14) = 76
2a = 76 - 42
2a = 34
a = 34/2
a = 17
