Answer
given,
high temperature reservoir (T_c)= 464 K
efficiency of reservoir (ε)= 25 %
temperature to decrease = ?
increase in efficiency = 42 %
now, using equation
[tex]\epsilon = 1 - \dfrac{T_C}{T_H}[/tex]
[tex]0.25 = 1 - \dfrac{T_C}{464}[/tex]
[tex]T_C= (1 - 0.25) \times 464 [/tex]
[tex]T_C= 0.75 \times 464 [/tex]
T_C = 348 K
now,
if the efficiency is equal to 42$ = 0.42
[tex]T_C= (1 - 0.42) \times 464 [/tex]
[tex]T_C= 0.58 \times 464 [/tex]
[tex]T_C= 269.12\ K [/tex]