申論題

4.Suppose that you currently have $40,000 invested in a savings account earning 3% per year compounded continuously. Market conditions are improving and you decide to continuously transfer 15% of the balance of your savings account into a stock fund earning 12% per year. You also withdraw $5,000 from the savings account each year for expenses.

(1)Set up and solve a linked pair of differential equations to determine respectively the amount of money in the savings account and stock fund t years from now.