Suppose that the supply function for honey is p​=S(q)=0.2q​+2.2, where p is the price in dollars for an 8​-oz container and q is the quantity in barrels. Suppose also that the equilibrium price is ​$4.40 and the demand is 3 barrels when the price is ​$6.40. Find an equation for the demand​ function, assuming it is linear.