Jane wants to buy a new house but needs money for the down payment. Her parents agree to lend her money at an annual rate of $4,$ charged as simple interest. They lend her for $5000,5$years. She makes no payments except the one at the end of that time.

Answer the following questions. If necessary, refer to the list of financial formulas.

$($a$)$ How much total interest will Jane have to pay?

$($b$)$ What will the total repayment amount be $($including interest$)?$