The amount A(t) of atmospheric pollutants in a certain mountain valley grows naturally and is tripling every 7.5 years.
(a) If the initial amount is 10 pu (pollutant units), write a formula for A(t) giving the amount (in pu) present after t years.
(b) What will be the amount (in pu) of pollutants present in the valley atmosphere after 5 years?
(c) If it will be dangerous to stay in the valley when the amount of pollutants reaches 100 pu, how long will this take?