Crystal Reports Formula Help (a "where statement", I think)

Message

     Hello, 
I have a table with data from multiple dates and accounts. 

I need to isolate the activity from one date and account, and display it on the same line as other accounts.  

For example: 

Account      Jan      Feb      Mar...  Total
1000            10         7         12        29
2000              5       10           8        23
3000            20       18         19        57
4000            11       11         11        33

In this case, account 1000 represents data that is a related to account 3000.  So, I need to be able to subtract the year to date (Jan-Mar) total of account 1000, from the monthly value of account 3000 for Mar (19-29).

I can't figure out how to write the formula where it uses a different account than the one on the associated line. 

I am guessing a where statement would work, but I don't know how to do that (if it can be used at all). 

Thanks, 

Paul