Use the internet! I can almost 100% guarantee that there is at least one forum out there dedicated to every single subject. The science crowd are also enormously driven by their intellectual ego and they would almost compete to answer any question you may have. Of course studying helps too!
You could see if your teacher could tutor you after class or you could hire a tutor to help you. You can purchase Chemistry help books online as well. Information based on the topic can be found for free on the internet. Just ask for help even if you are afraid to.
Try asking in friends in class if they would be willing to help you. You could also see if your school offered afterschool tutorial programs. Check the internet, too.
(1) Nitric Oxide is a common vasodilator for angina. It is oxidized to NO2 (g), according to the following reaction:
2 NO (g) + O2(g) 2 NO2 (g) H = - 114 kJ
Find the enthalpy, H, per gram of nitrogen dioxide, NO2(g).
