multiplication of a function with a Fourier-transformed equals to Fourier-transformed with a function
Hint:
You only need to use the definition of the Fourier transform and its inverse transform to show that if
$$G(f)=\mathscr{F}\{g(t)\}$$
then
$$g(f)=\mathscr{F}\{G(-t)\}$$
holds. Then just use the result from $b$.