Ok let's get started with this maths problem:
25 x 15 = Placeholder
25 x 15 = 357
so take the answer you have take it and plus it by 125
357 + 125 = your answer
so..
25 x 15 = 357 - 357 + 125 = 500
Now I know your asking how does 125 fit in with the sum well
25
25
25 +
25
___
100
then
100 + 25 = 1 Adult
So you need 6 Adults and 1 Child