Crystal Reports getting hours worked on weekends and holidays

Message

   hi experts
i need to create a formula to calculate how many hours did the contractor worked on the task, my data look like this:

Code           Contractor                            Date                             N/T    O/T

S49660
SECRETE STEPSSECRETE STEPS
2008-09-01 00:00:00.000
570
15

R04187
T.VTsuping
2008-12-01 00:00:00.000
90
210

R04185
T.VTsuping
2008-12-01 00:00:00.000
480
270

R04184
T.VTsuping
2008-12-02 00:00:00.000
480
180

and out of this date i need to work out the time that was worked on the weekend and holiday.
that means on the Normal Time field i have to create a function to calculate hours worked from Mon-Friday, Overt Time will be hours worked after 5pm then add another two fields for weekends and holidays