Average of a difference between 2 cels in a table/array

[GCRDelphi]

Hello,

I have the following columns:

A=Issue # B=User C=Issue D=Issue Date E=Start Date F=End Date

I want to create a table (for creating a graph) of the average per month if
the gap in days between column C and each of D E and F, for exmaple take an
everage of all the month of the results of Date in D - Date in C, and in the
next row E - C, etc.

Thank you for your help.