The relationship between the price (p) in dollars and the demand (x) in items for a product is given by the equation 2x² − 5xp + 70p² = 29,200. If the price is increasing at a rate of 4 dollars per month when the price is 20 dollars, what is the rate of change of demand with respect to time?
a) 0. 2811
b) 0. 4123
c) 0. 5342
d) 0. 6654