Ok, so
let 'n' be the number of times the boat has been rented.
Now, the member will pay: 40 + n*7.50
the non-member will pay: 12.50*n
we need to find n so that the member and the non-member would pay the same amount, so we equal both equations:

If we solve this equation for n:
5n = 40
and n=8
Therefore, n = 8 times