Hello there!

I am using Microsoft Excel to update an inventory list. I have three main columns as follows:
A2 represents the total number of boxes in the office and A3 represents the total in the basement.

A1 A2 A3

It has to follow these rules:
A1 represents a total amount equal to A2 + A3
When one box is brought into the office, the value in the column representing the basement amount should decrease. In other words, an increase (or decrease) in A3 should correspond to a decrease (or increase) by the same amount in A2.

How can I do this?

Thanks for your help!