You Have Been Hired as a Marketing Consultant to Johannesburg $q = m p + b$

You have been hired as a marketing consultant to Johannesburg Burger Supply, Inc., and you wish to come up with a unit price for its hamburgers in order to maximize weekly revenue. To make life as simple as possible, you assume that the demand equation for Johannesburg hamburgers has the linear form
$q = m p + b$
Where p is the price per hamburger, q is the demand in weekly sales, and m and b constants are certain constants you must determine. Your market studies reveal the following sales figures: when the price is set at $4 per hamburger, the sales amount to 1,420 per week, but when the price is set at $5 per hamburger, the sales drop to zero. Use these data to calculate the demand equation.

A) $q = 1,420 p + 8,520$
B) $q = - 1,420 p + 5,680$
C) $q = - 1,420 p$
D) $q = - 1,420 p + 7,100$
E) $q = 1,420 p - 7,100$