The initial rate of formation of and how long (in seconds) will take to decrease the concentration of P to have to be calculated.
Rate of a reaction: It represents the speed at which a chemical reaction runs. How much concentration of substrates (reactants) consumed and how much concentration of targets (products) formed in a unit of time is said to be rate of reaction.
Order of a reaction: The sum of exponents of the concentrations in the rate law for the reaction is said to be order of a reaction.
Rate: The rate is nothing but the change in concentration of substrate (reactant) or target (product) with time.