You have missed a ')':
warm_rate = (pow(warm_coffee + Kelvin),4)-(pow(room_temp + Kelvin),4);
should be:
warm_rate = (pow((warm_coffee + Kelvin),4)-(pow((room_temp + Kelvin),4);
You have missed a ')':
warm_rate = (pow(warm_coffee + Kelvin),4)-(pow(room_temp + Kelvin),4);
should be:
warm_rate = (pow((warm_coffee + Kelvin),4)-(pow((room_temp + Kelvin),4);