A small lake is stocked with a certain species of fish. The fish population is modeled by the function P = 10 1+ 4e-0.4t where P is the number of fish in thousands and t is measured in years since the lake was stocked. (a) Find the fish population after 4 years. (Round your answer to the nearest whole fish.) fish (b) After how many years will the fish population reach 5000 fish? (Round your answer to two decimal places. yr