What we need to do here is create an equation to solve.
the total cost of the trip was £591
this means that the amount for children + the amount for adults = 591
entrance fee was £12.35 for each adult and £8.75 for each child.
this means that our equation now is 12.35A + 8.75C = 591
the cost of hiring the coach was £118
this means we need to add this into our equation:
118 + 12.35A + 8.75C = 591
But we know how many children there are, 47. So we can plug in 47 for C then solve
118 + 12.35A + 8.75C = 591
118 + 12.35A + 8.75(47) = 591
118 + 12.35A + 411.25 = 591
12.35A = 591 - 411.25 - 118
12.35A = 61.75
A = 5
There were 5 adults in the group