E-a
No,the system can not be time-invariant.
Based on the data, if X has been delayed by 1, Y is not only delayed by 1,but also scale in the magnitude.
Since if we operate delay, the outputs won't match, the system is not time-invariant.
E-b
Since the system is linear, the input should be X[n] = u[n] in order to get Y[n]=u[n-1], where k=0
