A question about refrigerators and energy

[j88k]

Homework Statement

The coefficient of performance of a refrigerator is 5.40. The compressor uses 30.0 J of energy per cycle.

a) How much heat energy is exhausted per cycle?
b) If the hot-reservoir temperature is 27.0C, what is the lowest possible temperature in C of the cold reservoir?

Homework Equations

K=TC/(TH-TC)

QH = QC + Win

The Attempt at a Solution

solved part a) and found the energy to be 192 J

i keep on getting part b) wrong though and I ran out of chances to try.

please help!

 

[Redbelly98]

What is the COP (coefficient of performance) in terms of Qh, Qc, and/or W?