Answer:
65
Explanation:
Let "a" represent the number of adult tickets sold. Then the number of child tickets sold is 151-a and the total revenue for the day is ...
9.10·a + 5.10·(151-a) = 1030.10
4a = 260 . . . . . . subtract 770.10
a = 65 . . . . . . . . . divide by 4
The number of adult tickets sold on Monday was 65.
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Check
65 adult tickets and 86 child tickets will produce a revenue of ...
65·9.10 + 86·5.10 = 591.50 + 438.60 = 1030.10 . . . . answer checks OK