Create a state diagram to model the operation of a simple cell phone. The cell phone has an on/off switch. It has a numeric keypad that produces a keypad press event with a digit as its argument. The phone has a three-way switch that is set to ringing, vibrating, or both; it determines the action of the phone when a call comes in. The phone also has an action button that (a) initiates a call when seven digits have been entered, (b) answers a call when the phone is ringing or vibrating, and (c) terminates a call (hangs up) if a call is in progress. If the action button is pressed when fewer than seven digits have been entered and the phone is not ringing, the digits are erased (this is how dialing mistakes are corrected). Finally, the phone has a display that shows the digits that have been pressed so far, if any. Use at least one composite state in your model