percentage of time

I need formula for finding % of times... i have an employee that has worked 4.52 hours and was on break 16.50 minutes... need the percentage of the 4.52 he was on break.
Cells are in custom [h]:mm:ss format

4:52:45 | 16:50

I know simple math but cell format seems to messing me up as did and still doing with my previous problem... i cant change format of cells because im sending data to other parts of sheet in this format

Thankyou in advance!