In a Mobile Phone shop, a salesman earns a fixed salary of 3750 Dhs per month and a commission of 40 Dhs for every phone he sells. His gross salary can be calculated using the following formula: GS=40x 3750 where GS is his Gross Salary and x is the number of phones he sells. What is his gross salary for the Month of December if he sells 78 phones during the month