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 theres not enough money inserted, system requests for money.