Signaling Bandwidth
From Nyquist, we know that
i.e., our sampling rate must be at least twice the bandwidth of the signal to be reproduced.
This implies that the bandwidth of a PAM signal cannot exceed one half the signaling rate.
Since the signaling rate is 8,000 symbols per second, the bandwidth on the line will not exceed 4 Khz (minimum of two symbols per hertz of BW).