buyCoffees.scala

def buyCoffees(creditCard: CreditCard, n: Int): (List[Coffee], Charge) = {
  val purchases = (1 to n).map(i => buyCoffee(creditCard, i))
  val (coffees, charges) = purchases.unzip
  val reducedCharge = charges.reduce((c1, c2) =>
      Charge(c1.creditCard, c1.amount + c2.amount))
  (coffees, reducedCharge)
}