x=number of adult tickets
y=number of children tickets.
we can suggest this system of equations:
x+y=170
8.7x+5.4y=1224.90
We can solve this system of equations by substitution method:
x=170-y
8.7(170 - y)+5.4 y=1224.90
1479-8.7y+5.4y=1224.90
-3.3 y=1224.90-1479
-3.3 y=-254.1
y=(-254.1) /(-3.3)
y=77
x=170-y
x=170-77
x=93
Answer:93 adult tickts were sold that day.