FIND C! What is the unit price at that level of demand?

FIND C! What is the unit price at that level of demand?

The demand function for the Luminar desk lamp is given by the following function where x is the quantity demanded in thousands and p is the unit price in dollars.

p=f(x)= -0.1x^2-0.7x+33

(a)Find f’(x)

f'(x) = -.2x-.7

(b)What is the rate of change of the unit price when the quantity demanded is 4000 units (x = 4)? 

$-1.5per 1000 lamps 

(c)What is the unit price at that level of demand?