Answer: 26 child tickets were sold that day.
Explanation:
Let's say the number of child tickets sold is "x".
According to the problem, the number of adult tickets sold is four times the number of child tickets sold. So, the number of adult tickets sold would be 4x.
6.10x + 9.90(4x) = 1188.20
6.10x + 39.60x = 1188.20
45.70x = 1188.20
x = 26