Given:
Th = 270 °C = 270+273 = 543 K, hot temperature
Tc = 180 °C = 180+273 = 453 K, cold temperature
According to the Carnot theorem, the maximum efficiency achievable by a heat engine between a hot and cold temperature is
η = 1 - Tc/Th
= 1 - 453/543
= 0.166 = 17% (approx)
Answer: 17% (nearest integer)