What is the answer to this problem 90-40.74

Element x decays radioactively with a half life of 8 minutes. if there are 450 grams of element x, how long, to the nearest tenth of a minute, would it take the element to decay to 37 grams?

Aculture started with 2,000 bacteria. after 8 hours, it grew to 2,400 bacteria. predict how many bacteria will be present after 19 hours . round your answer to the nearest whole number. p=ae^kt

How many quarts of a 50% solution of acid must be added to 20 quarts of a 20% solution of acid in order to get a 40% solution of acid?