how many grams of water can be formed when 28.7 grams of CH4 reacts with 45.8 grams of O2

Answer 1

See your problem above. This one is a limiting reagent problem because BOTH reactants are given. What you do is to solve the stoichiometry problem twice, once with the CH4 amount and once with the O2 amount. You will get two answers for the moles H2O formed and the correct answer is the the smaller of the two.