Hello and welcome to the forum,
Just curious. . .
Why would you believe that a redefinition of some PIC X field as a PIC 9 field would transform the alphanumeric value to something usable as a numeric?
Something very basic has been completely overlooked. . .
1. Can we redefine variables with different data types?
2. If yes then why can't we perform computation on it?
1. Yes, but should only do so when a data item has multiple definitions/uses. . .
2. Because computations require valid numeric values. . .
The manuals can surely help, but you would benefit by doing some basic review with your seniors or whoever was the COBOL instructor.