April borrows $18000 at an interest rate of 5% to purchase a new automobile. At what rate (in dollars per year) must she pay back the loan, if the loan must be paid off in 5 years? Set up the differential equation as in Exercise 20.

Data From Exercise 20

Sam borrows $10000 from a bank at an interest rate of 9% and pays back the loan continuously at a rate of N dollars per year. Let P(t) denote the amount still owed at time t.