6. Andres deposited $10,000 in a savings account. After 8.25 yr, the value of his account had doubled. a) Find the function in base 2 that models the value, A(t), of Andres's account after t years. b) Rewrite the model from part (a) using base e. c) What is the yearly percentage growth rate of the account? d) Find A'(12), and interpret its meaning. 7. After a large manufacturing plant closed, Parsonville's population decreased by 20%. every 3 yr. Assume that the population was 7500 when the plant closed. a) Find the function in base 0.8 that models the population, P(t), of Parsonville t years after the plant closed. b) How much time is need for Parsonville to lose half of the population it had when the plant closed? c) Find P'(8), and interpret its meaning.