Find the impulse response function of a system whose equation of motion is given by

(a) \(\dot{x}+4 x=f(t)\)

(b) \(\ddot{x}+4 x=f(t)\)

(c) \(\ddot{x}+5 \dot{x}+4 x=f(t)\)

(d) \(\ddot{x}+2 \dot{x}+x=f(t)\)

(e) \(\ddot{x}+5 \dot{x}+4 x=5 \dot{f}(t)+4 f(t)\).