3.7-4. Given the signal e(t) = 3 sin 4t + 2 sin 7t. (a) List all frequencies less than w = 50 rad/s that are present in e(t). (b) The signal e(t) is sampled at the frequency ws = 22 rad/s. List all frequencies present in e*(t) that are less than w 50 rad/s. (c) The signal e*(t) is applied to a zero-order hold. List all frequencies present in the hold output that are less than 50 rad/s. (d) Repeat part (c) for e*(t) applied to a first-order hold.