I’m not sure whether there is a typo in the function but I might have the answer.
If f(x) = 5(x+1)+3 = -12 then you can solve for x.
5(x+1)+3 = -12
5x + 5 + 3 = -12 << expand the brackets
5x + 5 = - 15 << minus 3
x + 1 = -3 << divide everything by 5
x = -4 << minus 1
I don’t know if this helps x Sorry
