The outputs of four systems (S₁, S₂, S₃ and S₄) corresponding to the input signal sin(t), for all time t, are shown in the figure.

Based on the given information, which of the four systems is/are definitely NOT LTI (linear and time-invariant)?

A continuous-time filter with transfer function $$\,H(S) = {{2s + 6} \over {{s^2} + 6s + 8}}$$ is converted to a discrete time filter with transfer function $$G(Z) = {{2{z^2} - 0.5032\,z} \over {{z^2} - 0.5032z + k}}$$ so that the impulse response of the continuous-time filter, sampled at 2 Hz, is identical at the sampling instants to the impulse response of the discrete time filter, The value of k is _________________________.

A first-order low-pass filter of time constant T is excited with different input signals (with zero initial conditions up to t = 0). Match the excitation signals X, Y, Z with the corresponding time responses for $$t\, \ge 0$$:
X: Impulse P: 1 $$ - {e^{ - t/T}}$$
Y: Unit step Q: t $$ - T(1 - {e^{ - t/T}})$$
Z: Ramp R: $${e^{ - t/T}}$$