Heat Transfer (Renewable Energy Sources) conundrum

[jbh393]

In my renewable energy sources class I've been stuck on this problem, and it doesn't help that the book itself is vague and doesn't really allude to any examples pertaining to this. I've attached my work and problem, and I'm trying to see if someone could nudge me in the right direction because I'm completely lost. The answers were suppose to be 2.7 and 650 but I can't get that nor can I understand where to go.