A student makes loan of $$135,581$ and agrees to pay back within $20$ years with $2\mathrm{.}5\%$ interest. Assume that payment happens once a year.

$1.$ Calculate the payment for each year.

$2.$ What is his$/$her total payment including interest rate?

$3.$ If the rate goes up to $4\%,$ what is his$/$her total payment including interest rate?