prepare a level $0$ physical DFD for the following process. A customer sends an order document to a company. A clerk, Mary solis, in the sales department enters the data from the cusstomer order document into the computer system. After keying in the data, the customer order document is filed in the sales department by customer number. A sales department manager, Kip Muller, processes the entered data by checking customer's credit by referring to the customer file and by checking inventory availability by referring to the inventory file. This process laso produces a transaction file. The transaction file is then processed by John Edge who records the transaction data to a sales order file and produces three paper copies of a sales order. Copy $1$ is sent to the warehouse; copy $2$ is sent to the shipping department; copy $3$ is sent to the billing department