economic production quantity

okay this math is related to operations management, i am having a real tough time with this one:

The friendly sausage factory(fsf) can produce hot dogs at a rate of 5000 per day. fsf supplies hot dogs to local restuarants at a steady rate of 250 per day. The cost to prepare the equipment for producing hot dogs is $66. Annual holding costs are 45 cents per hot dog. The factory operates 300 days a year. Find

a. the optimal run size

b. the number of runs per year.

c. the length ( in days) of a run.

The correct answer for optimal run size should be 4,812

to find optimal run size you need to find

D=demand usualy in units per year

S= setup or ordering cost

H= holding 9carying0 cost per unit

p= production or delivery rate

u=usage rate