Question

let f(x)=x+2/x+8. what does f^-1(-4) equal?

Answer 1

if y = (x+2)/(x+8), (notice I assumed you have a typo)
the inverse would be
x = (y+2)/(y+8)
sub in x = -4 and solve for y

(I get f^-1(-4) = -34/5)

Answer 2

yes it is. Thank you very much for your help.