Question

You borrow $500 to buy a computer. The simple interest rate is 15%. You pay off the loan after 4 years. How much do you pay for the loan?

Answer 1

Here the interest would be  i = P*r*t, or, specifically,

interest on loan = i = ($500)(0.15)(4 yrs) = $300.

This assumes just ONE repayment:  $300 plus $500, or $800, after 4 years.  It's much more common to repay a loan like this with monthly payments.