Suppose the quantity (in grams) of a radioactive substance present at time t is Q(t) = 10,000 (5 - 0.21) where t is measured in months. a. How much will be present in 7 months? b. How long will it take to reduce the substance to 16 grams? a. There will be grams of the substance present in 7 months. (Round to the nearest gram as needed.) b. It will take months to reduce the substance to 16 grams. (Round to the nearest month as needed.)