Uhh... is this the full problem because this looks like this is half a problem.
The answer is 43-30x because you always add the parenthesis first which now you have 18+25-10x3 then you calculate the product 18+25-30x. after all that you then add all the numbers and get 43-30x. hope this helps
So just switch x and y to get:

and solve for x.
so f(-1) = x = 2y -10