We Wish to Increase the Efficiency of an Ideal Heat

We wish to increase the efficiency of an ideal heat engine from 25% to 35%. If the initial temperature of the hot reservoir is 650°C, to what temperature would this need to be increased assuming the exhaust temperature remains the same?

A) 1065°C
B) 910°C
C) 1019°C
D) 973°C
E) 792°C