let f(x)= (x+4)/(x+6)

Remember that some x value led to -8

So.....we can solve this to find f^-1(-8)

(x + 4) / ( x + 6) = -8

x + 4 = -8 (x + 6)

x + 4 = -8x - 48

9x = - 52

x = -52/9    =  f^-1(-8)