Place the cursor at the blank cell of the first row then click layout Formula see screenshot. Next enter the number or cell reference that you want and then click OK. Then all the left.
Click in a cell that should contain the sum of the rows.
A dialog named Formula is displayed typing SUMLEFT in the formula text box. To do this click inside the last cell in the fourth column click on Layout in the ribbon and then click on Formula at the far right. Sum a row of a table in Word. Type the left bracket that you want to appear around the equation number.