x = child tickets
y = adult tickets
x + y = 141
5.60x + 9.30y = 974.60
y = 141 - x
5.60x + 9.30 ( 141 - x ) = 974.60
5.60x + 1311.3 - 9.30x = 974.60
-3.70x + 1311.3 = 974.60
-3.70x = 974.60 - 1311.3
-3.70x = -336.7
x = 91
91 child tickets were sold that day