14.8 weeks - i want it to say 15 weeks

Hello :-)

How do i get the duration to show just whole numbers e.g. 15w not 14.8w

The project is Mon to Fri 9-5pm.

I need to show the completion date as a friday not a sunday but still have the week as a whole number.

I have Sat & Sun as none working days in the project calendar.

Some tasks it works and some it doesn't and i can't undersatand why.

Please help :-)

Thanks