How to calculate the percentage of hours entered for a project per user?

Scenario:

• User A is part of Project 1, Project 2 and Project 3.
• User has entered 10Hrs for Project 1, 20Hrs for Project 2 and 20Hrs for Project 3.
• Admin wants to generate a report giving him the % breakdown of the User's time consumed per project/task.

Resolution:

• A custom column which has the Billable + Non-Billable Hrs as the numerator and Total Hrs Period as the denominator. 
• Group the report first by username and then by project name to get the desired layout of the report.
• Use the following formula in the report custom column,

(100*(BillableHours+NonBillableHours))/TotalPeriodHours