Question

The profi t, P, in thousands of dollars, from the
sale of x kilograms of coffee can be modelled
by the function P(x) __
4x  200
x  400 .
a) Sketch a graph of this relation.
b) The average profi t for a given sales level, x, can
be found by drawing a secant from the origin
to the point (x, P(x)). Explain how average
profi t is related to the slope of a secant.
c) Estimate where the average profi t is the
greatest. Verify using slopes.
d) Determine the rate of change of the profi t
at a sales level of 1000 kg.

i get a and b but i dont get c and d