To go on a summer trip, Milan borrows $$600.$ He makes no payments until the end of $6$ years, when he pays off the entire loan. The lender charges simple interest at an annual rate of $4\%.$Answer the following questions. If necessary, refer to the list of financial formulas.?$($a$)$ How much total interest will Milan have to pay?$ $(6)$ What will the total repayment amount be $($inciuding interest$)?$