Answer:
Arrange All
Step-by-step explanation:
For him to to view them all at the same time, so he should use the Arrange All
command. To do this, you will need to
Open the workbooks that is needed to arrange, in this case at least two workbooks are to be opened, then make selection of the worksheet in each workbook that is needed to be displayed, then on the view tab, you can make selection of "Arrange All button" in the Window.