Question 10 is the decomposition of water. The left side is 2 water molecules, while the right side is two hydrogen molecules and 2 oxygen molecules.
Question 11 consists of calculating the amounts of atoms on each side. Since the left side has 6 hydrogen atoms, the right side must as well. On the right side, hydrogen has a 2. So divide 6 by 2 to find the coefficient (3). You can confirm the answer by confirming the oxygen is the same on both sides (it is).
