At a Price Of $\$ 2.80$ Per Gallon, the Average Weekly Demand by Consumers for Gasoline

Multiple Choice

At a price of $\$ 2.80$ per gallon, the average weekly demand by consumers for gasoline is 42 gallons. If the price rises to $\$ 3.00$ , the weekly demand drops to 39 gallons. Assuming demand is linear, let $Q=b+m p$ , where $Q$ is the weekly quantity of gasoline demanded and $p$ is the price per gallon. What is the slope $m$ , along with its economic significance?

A) -0.60 ; if gasoline prices increase by $\$ 1$ per gallon, then there will be a 0.60 gallon decrease in weekly demand.
B) -3 ; if gasoline prices increase by $\$ 1$ per gallon, then there will be a 3 gallon decrease in weekly demand.
C) -15 ; if gasoline prices increase by $\$ 1$ per gallon, then there will be a 15 gallon decrease in weekly demand.
D) -0.20 ; if gasoline prices increase by $\$ 1$ per gallon, then there will be a 0.20 gallon decrease in weekly demand.