Prepare the user interface elements for a coffee vending machine with following features: Assume a machine for coffee and a cup of coffee costs 2 quarters. The machine accepts only quarters (if another type of coin is inserted it is returned to customer mechanically and no message is given, so ignore that case). The machine works in a way that the customer first needs to insert quarters. The vending machine memorizes the number of quarters inserted and displays the amount. The customer needs to press a button representing coffee. The machine never runs out of coffee. If right amount is inserted, the machine gives the customer coffee. With a message specifying that coffee is ready. If the amount inserted into the machine is greater than the cost of coffee the machine returns the change. The machine also has a button for returning the money inserted which can be pressed any time. If the customer presses the coffee button and there's not enough money inserted, system requests for money