Crystal Reports How to divide the field,depending on number lines

Message

   I have a report with more details how split the field from the database that begins in the Detail a to continue after specified number of lines in the second detail, and then in the third ... (1 field - more details)
Example:
I need to split the field with 100 lines to 3 detail;
Detail a: 1 to 40 lines
Detail b: 41 to 80 lines
Detail c: 81 to end.
Thx 

Edited by denhors - 25 Jan 2011 at 3:11am