Trying to divide specific cells in one column by specific cells in another column in Summary Sheet.

Hello, I'm trying to divide cells in one column by cells in another column. After reviewing several similar questions I created this formula:

=SUM([SOR - # of Users Activated]72:[SOR - # of Users Activated]75 / SUM[SOR - # of Users Ordered]72:[SOR - # of Users Ordered]75)

This of course is not working, Could you advise if this can indeed be done and if so how I should change my formula, it is returning 'Invalid Operation'