Here you go, this should work.
* @desc Calculates the monthly payments of a loan
* based on the APR and Term.
* @param Float $fLoanAmount The loan amount.
* @param Float $fAPR The annual interest rate.
* @param Integer $iTerm The length of the loan in months.
* @return Float Monthly Payment.
function calculateMonthlyPayments( $fLoanAmount , $fAPR, $iTerm )
echo calculateMonthlyPayments( 100, 8.9, 12 );