6A
$ \,x(t-k) \to System \to y(t)=(k+1)^{2}x(t-k-1)\, $
Proof:
$ x(t-k) \to System \to y(t)=(k+1)^{2}x(t-k-1) \to Time Shift(t0) \to z(t)=y(t-t0) $
$ \, =(k+1)^{2}x(t-t0-k-1)\, $
$ x(t-k) \to Time Shift(t0) \to y(t)=x(t-t0-k) \to System \to z(t)=(k1+1)^{2}y(t-k1-1) $
$ \, =(t0+k+1)^{2}x(t-t0-k-1)\, $
It is not time invariant.
6B
If superposition works, integrating input will yield integration of output, integration of $ u[n-1] $ is \delta [n-1], thus u[n] as an input will yield the desired output.
