The function works as follows:
If, for example, we want to produce 100 parts, the total cost is calculated as follows:
c(100)=12.5*100+4,500=1,250+4,500=5,750 (dollars, or some other unit).
We note that if p=0 (that is, if no parts are produced) then
p(0)=12.5*0+4,500=0+4,500=4,500.
Thus, 4,500 represents the initial costs, without producing any part.