In a chemical reaction the products are found at the right of the equation, the products are what is being made once the reaction is complete. On the right side if the chemical equation is the reactants or starting materials, these are the substances that are combined to provide a product on the right side of the equation. Since I am not able to see the equation, just simple add all the carbons that are on the left and that will tell you how many carbons there are in total on the reactant side and if you add all of the carbons on the right side it will let you know how many carbons there are on the product side. The same steps can be taken for Oxygen.
I am unable to answer the last one as I need more information. But basically the law states that any system for which matter and energy cannot be transfer as it is a closed system, then since the system's mass can't change then it cannot be added or subtracted