calculus help

[dolphin6]

If the price charged for a bolt is p cents then x thousand bolts will be sold in a certain hardware store, where p=130-x/14. How many bolts must be sold to maximize revenue?

 

[Gene]

The profit is xp.
set the derivitive of x(130-x/14) = 0

 

[dolphin6]

don't understand

I still don't understand could you work it out for me
Thanks

 

[Gene]

Now you worry me. Are you saying you don't know how to take the derivitive? P is the profit.
dP=d(130x-x²/14) =
dP/dx = 130-2x/14 = 0
x = 14*130/2 = 910 thousand bolts (at 6.5¢ per bolt marked down from 13¢ each)