Right choice is (c) 50dB
Easy explanation: The total gain of a cascading transistor amplifier is the sum of the multiple stages when the gain is calculated is decibels. Given, AV1 = 14dB, AV2 = 12dB and AV3 = 24dB
AV = AV1 + AV2 + AV3 = 14dB + 12dB + 24dB = 50dB