Answer:
reservoir is 727°C, then low temperature
Step-by-step explanation:
Efficiency for any Heat engine = Work done by engine / Heat provided to the engine
Also, for a carnot engine derived formula for Carnot Engine
= 1- T2/T1
Where, T2 = sink reservoir temperature
and T1 = source reservoir temperature
727° C = 1000 K
So, 0.75 = 1-T2 / 1000
So, T2 = 1000*0.25 = 250 K = -23 Kelvin