3. Consider a discrete-time LTI system with impulse response h[n] = [1,2,3] starting at time n = 0. (a) Find the output of the system given the input r[n] = [1, 1, 1, 1] starting at time n= 0. (b) Use part (a) to find the output of the system given the input r[n] = [1, 1, 2, 2, 1, 1] starting at time n = -2. if n > 0, 0 ifn < 0. (c) Find the output of the system given a step function as input, i.c., a[n] =