How to set damage by formula

How can I set weapondamagepct = 100 + (skill level * 5)? I want to use the formula

Please tell more what you want. Not so many templates allow use forulas directly.
As I can suggest, You need set weapon damage for custom skill. In this case Open weaponDamagePct parameter, add as more values as your skill need, set value to 100 and then Inc.Series to 5. Obtained array will corresponds to formula you need.