Refund for partially used service

mediumbillingJavaScript

A customer paid upfront but only used part of the service. Refund the unused portion.

partialRefund(paid: int, usedUnits: int, unitPrice: int) → int

Where you start

function partialRefund(paid, usedUnits, unitPrice) {
  
}

Multiply usage by price, subtract from what was paid, and clamp.

Reference solution in JavaScript

function partialRefund(paid, usedUnits, unitPrice) {
  const cost = usedUnits * unitPrice;
  return paid > cost ? paid - cost : 0;
}