A company is increasing the production of a product at the rate of 20 units per week. The demand and cost functions for the product are given by

p = 50 0.01x

and

C = 3000 + 40x 0.03x²,

where x is the number of units produced per week. Find the rate of change of the profit with respect to time (in dollars per week) when the weekly sales are

x = 700 units.