For the gas station system, draw an internal block diagram to depict how the subsystems of the point of sale system and the fuel delivery system interact. You will need to use nested parts (i.e. internal structure) to show the subsystems of the point of sale system and the fuel delivery system. Include the following interactions: 1. Each cashier station provides a cash payment service* to a cashier. 2. Each cashier station interacts with the central controller to authorize a cash purchase. 3. Each customer station provides a credit/debit payment service* to the customer. 4. Each customer station interacts with the central controller to get authorization for credit/debit purchases and receive authorization for cash purchases. 5. The central controller uses a credit/debit purchase authorization service* provided by financial institutions. 6. Each customer station is paired with one fueling station and informs the fueling station when a fuel purchase has been authorized. 7. Each fueling station provides a fuel grade selection service* to the customer. 8. Fueling stations receive fuel from a fuel tank determined by what grade fuel was selected by the customer. 9. After a fuel purchase has been authorized, a fueling station dispenses fuel to the customer's vehicle. 10. When the customer is finished fueling, the fueling station informs the customer station a summary of the fuel dispensed. Show the external actors as Reference Properties (i.e. dotted rectangles). In Papyrus the Reference Property name cannot exactly match the actor name so use some variation on the actor names for the Reference Property names. Note that behavior (i.e. the conditions for doing something or the sequence of actions) are not part of the syntax of an internal block diagram and do not need to be shown on this diagram. * For this assignment, it is not necessary to show the popsicle symbol for services provided by a port nor the socket symbol for services required by a port. Just show it as a simple port with a name that reflects the service provided or required by that port.