Refer again to the data from the Gilmore Accounting firm found in the Excel file Gilmore. $($a$)$ Incorporate the client type into the regression analysis using dummy variables. Describe the resulting multiple regression estimate.$($b$)$ Test to determine if this model is useful in predicting the net profit earned from the client.$($c$)$ Test to determine if the number of hours spent working with the client is useful in this model in predicting the net profit earned from a client.$$