Correct option is (a) 0.68
To explain I would say: The voltage gain AV of a simplified common collector amplifier configuration can be calculated using AV = RE / (RE + re‘) . Given, RE = 25kΩ and re‘ = 12kΩ:
AV = RE / (RE + re‘) = 25 / 25 + 12 = 25 / 37 = 0.675 ≈ 0.68