You can use the AVERAGE function to find the mean average cost of all entertainment for January and February.
Excel will enter the formula for you. Click in cell D7. On the Home tab, in the Editing group, click the arrow on the Sum button, and click Average in the list. The formula =AVERAGE(B7:C7) appears in the formula bar near the top of the worksheet.
You could also type the formula directly into the cell.
Note The Sum button is also located on the Formulas tab, in the Function Library group.