Frequency response of each component of a system given its global response
With feedback systems such as the one given it's often easy to define an additional signal at the output of the adder. This gives the following equations:

$$U(f)= X(f)-H_2(f)Y(f)\tag{1}$$

and

$$Y(f)=U(f)H_1(f)\tag{2}$$

Now you can solve Eqs $(1)$ and $(2)$ to get the frequency response $H(f)=Y(f)/X(f)$.