Creating Validation Calculation for DFF fields

Hi,

As we are trying to create the DFF field level validation in the requisition creation page for the below requirement.

Field 1 - Duration of Requirement in Month
Field 2 - Total available budget inclusive of agency fee in QAR
Field 3 - Total Monthly budget inclusive of agency fees in QAR

Based on the Field 1 value and field 2 value needs to be calculated and store the output value in Field 3.

"Duration of Requirement in Month" = 5
"Total available budget inclusive of agency fee in QAR" = 5000
Total Monthly budget inclusive of agency fees in QAR = 5000/5 = 1000(this 1000 should populate in field - "Total Monthly budget inclusive of agency fees in QAR")