Answer:
91 adult tickets
Explanation:
Algebra is really useful here:
Let a = number of adult tickets sold and c = number of child tickets sold.
Thus, we can say that
a + c = 153 (number of tickets)
6.40c + 9.60a = 1270.4. (cost of all of the tickets)
Solving,
c = 153 - a
6.40(153 - a) + 9.60a = 1270.4
979.2 - 6.40a + 9.60a = 1270.4
3.20a = 291.2
a = 91