We Wish to Increase the Efficiency of an Ideal Heat $\circ$

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 ^$\circ$ C,to what temperature would this need to be increased assuming the exhaust temperature remains the same?

A) 1065 ^$\circ$ C
B) 910 ^$\circ$ C
C) 1019 ^$\circ$ C
D) 973 ^$\circ$ C
E) 792 ^$\circ$ C