Step-by-step explanation:
You can call c the number of children and a of adults; you get:
5.20c+8.50a=1097.60
and
a=4c meaning that the number of adults was four times the children.
Substituting this value of a into the first equation we get:
5.2c+8.5(4c)=1097.6
5.2c+34c=1097.6
rearranging:
c=1097.639.2=28
and so:
a=4c=4⋅28