What is the total bandwidth of an FM phone transmission having 5 kHz deviation and 3 kHz modulating frequency?

Explanation

Carson's rule gives total FM bandwidth as 2 × (deviation + highest modulating frequency) = 2 × (5 + 3) = 16 kHz. The 8 kHz choice is the sum inside the parentheses and forgets that sidebands appear on both sides of the carrier.