Let us use the CT LTI system:
$ y(t) = x(3t) + x(t+3) $
The impulse response, h(t), of this system is computed using the following:
$ x(t) = \delta (t) $
$ h(t) = \delta (3t) + \delta (t+3) $
The signal used in question 1:
$ x(t) = 3cos(4\pi t) + e^{j\frac{2\pi}{5}t} $
