Answer 2.8

The formula for channel capacity in a baseband channel (i.e. the useable bandwidth extends from 0 Hz to B Hz is given by:

Channel Capacity C = 2Blog2M

Thus for 28.8 kbps in 3.1 kHz, the number of symbol states required M is:

M = antilog228800 / (2 x 3100) = 22.8 or 23 symbol states