Okay so I have to balance these equations.But I don't really understand how to and how to find the answers...

I will explain 1 below.

Explanation:

CH4 + O2 = CO2 + H2O.

You cannot ever change the existing elements in a balancing equation. You can also never make the quantity of the element or molecule smaller than it's original size. However, you can add numbers to the left of an element to multiply it's amount to balance an equation. For this equation, we have one C, 4H, and 2O on one side, and one C, 3O, and 2H. The C is balanced because each side has one, so we can leave that alone. However, the O and H are unbalanced. This equation is quite simple, all we have to do is add a 2 to the H2O on the right side of the equation to make it 4H (which balances). However, the right side now has 4O, so we can now just multiple the O2 on the left side by 2 in order to have 1 C, 4 H, and 4 O on each side. That would look like this: CH4 + 2O2 = CO2 + 2H2O.