Help with the creation of a report

Help with the creation of a report

Hello,

We need a report "Hours by projects" with a way to reduce the hours by 20% if the employee is a junior. I would like to see the last column with the adjustments and the previous one with the real hours.

I've tried with a customizes field in Staff and a calculation but it doesn't work.

The time entries and the projects are both made in Zoho Books.
 
Thanks for your help,