An average is defined as y (t) = HITx(T)dT where 7 > 0 is the averaging interval, x(t) and y(t) are the system input and output. a) Determine if the average is a linear system. b) Let x(t) = u(t), calculate and the output, delay then the input to get x(t-2) = u(t-2), and calculate the corresponding output. Does the system seem time invariant? Explain. c) Is this system causal? Explain