Step 5.   In Cell B12 type in the = Average Formula:

                                        =AVERAGE(B3:B11)     Press Enter

An error message will appear.            That's good!

Step 5a.Use the "skinny plus " to extend the Average Formula to the right for the entire row.

Select Cell B12 > Move your mouse around until it changes to a "skinny plus." >
Click > Hold >Drag to the left >until you reach J12 > Release.