Data in hours format calculates wrong

Hi, We have an existing overtime form that I have tried to modify. A need for our guys to work overnight required an additional column, 'C',in the attached sheet. I have managed to overcome working past midnight and get the hours in column 'C' but when I try to add up those hours, that is where it is going wrong.
C28 should total 27 hours, it is showing 1683.
C29 is the total hours x 1.33 - it should be 35.91, it is showing 2238.4
C30 is the number of nights worked, in this case 3
C31 is the number of normal working hours multiplied by the number of nights
C32 should be the resultant overtime worked - should read 11.91 but shows 2214.4
I have checked the formatting and cannot see what is wrong, so any help appreciated. I am aware that there are a few other errors when certain combinations are selected, I can deal with those.
Thanks,
Cliff