If f (x) is differentiable at point X and lim f (x-3h) - f (0) / h = 1, then f '(x) =? H-0

If f (x) is differentiable at point X and lim f (x-3h) - f (0) / h = 1, then f '(x) =? H-0

lim f(x-3h)-f(x)/h
=(-3) lim ( f(x-3h)-f(x) )/(-3h)
=(-3) lim ( f(x-3h)-f(x) )/(-3h -0)
=(-3) f'(x)
That is (- 3) f '(x) = 1
f'(x)= -1/3