Hi. so apparently I am reviewing for my exams hence it would be better to practice solving on your own.

so i started answering some questions and I got stuck with this problem. the question goes with answer and a "general solution" so I am on the part of deciphering it how does the solution ended up to such value.problem is, we get different answers on getting delta H: i got -1513.69 btu/lbm, the solution goes with -99 btu/lbm. can someone please help me what have i done wrong?

Thank you very much.