Variable past

[jakk100]

I have data that has variable Dates. Example:
OP 4         12/2608
OP 5          12/30/08
OP 6          1/5/09
What I want to do:
See the date from the prior OP 5 next to the date for OP 6. (The prior date is variable so I cant do a simple subtraction.)
Example:
OP 4         12/2608   
OP 5          12/30/08    12/26/08
OP 6          1/5/09         12/30/08
Does that make sense?
I use Impromptu and am a beginner.
Thank you.