basicaly the inverse switches x and y
so finverse(8)=? means that f(?)=8
that might not make sense to you but I know that
what that means is we just need to solve the equation
8=(x+5)/(x+10)
so
multiply both sides by x+10
8(x+10)=x+5
8x+80=x+5
minus x both sides
7x+80=5
minus 80 both sides
7x=-75
divide both sides by 7
x=-75/7
f⁻¹(8)=-75/7