Finding Average Rate of Reaction

Rate of reaction is a measure of how fast a reaction occur, or how much the reactant/product change in a period of time.
Rates of reaction =  Quantity change of reactants/products Total time for the reaction
In a chemical reaction, 2.5g of calcium carbonate react completely with excess hydrochloric acid to produce 600cm³ of carbon dioxide gas in 1.5 minutes. Find the rate of reaction in term of
a. decreasing mass of calcium carbonate
b. increasing volume of carbon dioxide gas produced

Change of the amount of reactant=-2.5g Tima taken for the change=1.5minute=90s Rate of Reaction = -2.5g 90s 0.027g s -1
Change of the amount of product=600c m 3 Tima taken for the change=1.5minute=90s Rate of Reaction = 600c m 3 90s 6.7c m 3 s -1