Computing ActivityDriverTargetValue using Rule

Hi,

I am trying to calculate ActivityDriverTargetValue using a rule.

Say I have version1 and version2 and I want ActivityDriverTargetValue of version2 is 1.2 times of ActivityDriverValue of version1.

simply put, ActivityDriverTargetValue(version2) = 1.2*ActivityDriverValue(version1)

How can I calculate this using a rule.

Thanks,

Nagadeep