Calculated field, please, help!

I really need to use calculated field, for calculate commissions, but i tried and i tried to build worflow but i don’t know how is the correct syntax. Someone could help me?

Thanks in advance

See here:
https://suitecrm.com/forum/developer-help/12853-what-is-workflow-calculated-fields-contributed-by-diligent-technology-business-consulting-gmbh#43457