// add a parameter called milesTraveled to the function
// taxiFare
var taxiFare = function () {
  var baseFare = 2.50;
  var costPerMile = 2.00;
  var milesTraveled = 4;

  // calculate cost using baseFare, milesTraveled, and
  // costPerMile
  var cost = (baseFare) + (milesTraveled) * (costPerMile);

   return cost;
};