How to work out number of 'days' worked based on total hours

So I have a situation where we work out the number of base, overtime at 1.5x and overtime at 2x for a job which is charged in number of hours. A full day is 12 hours, any additional hours is in a second day.
From 0-8 hours is base rate, 8-10 hours is OT1.5 and 10-12 is OT2
Examples:
A job at 21.5 hours would be 16x base, 3.5x OT15 and 2x OT12.
A job at 26.54 hours, would be made up of 18.54x base, 4x OT15 and 4x OT2

What formulas or functions can I use to automatically tell me how many hours of base, OT15 and OT2 are needing to be billed?