Answer: 68 child tickets were sold
Explanation:
Let x represent the number of child tickets that were sold that day.
Let y represent the number of adult tickets that were sold that day.
A total of 124 tickets were sold on Tuesday. This means that
x + y = 124
At the city Museum child admission is $5.70 and adult admission is $9.80. The total sales from tickets was $936. This means that
5.7x + 9.8y = 936 - - - - - - - - -1
Substituting x = 124 - y into equation 1, it becomes
5.7(124 - y) + 9.8y = 936
706.8 - 5.7y + 9.8y = 936
- 5.7y + 9.8y = 936 - 706.8
4.1y = 229.2
y = 229.2/4.1
y = 55.9
y = 56
x = 124 - y = 124 - 56
x = 68