Method add

strings/ReceiptBuilder.java:17–20

(String name, int qty, double price)

      "%-15s %5s %10s%n", "----", "---", "-----");
  }
  public void add(String name, int qty, double price) {
    f.format("%-15.15s %5d %10.2f%n", name, qty, price);
    total += price * qty;
  }
  public String build() {
    f.format("%-15s %5s %10.2f%n", "Tax", "",
      total * 0.06);