Correção de texto: E-mail to a friend

Hey buddy, how are you doing?

We are studying Organizational Behavior at the moment. We have 5 subjects each semester.
We had a great trip yesterday, nice lunch at a great hotel and so forth. On the other hand it was really hot, my dad's truck has no air-conditioner so had a hard time going and coming back.
About my grades, my average is 8 to 9 out of 10 !

Tonight I will read the e-mails you sent me and then I'll e-mail you my opinion.

As soon as you have spare time, feel free to correct my mistakes !