1- Reactants (H = 2, O = 2)
Products (H = 2, O = 0)
2- Reactants (P = 4, O = 2)
Products (P = 2, O = 3)
So basically if it was H20, then there is 2 Hydrogen because the two is in front of the H and there isn’t a 2 in front of Oxygen.
However if it was H2O2, then there is two hydrogen and two oxygen because there is a two on both of the symbols which indicates how much reactants/products there is.
Hope this helps!