Final answer:
The social marginal benefit of firework consumption is found by horizontally summing Barton's and Jay's demand functions, resulting in the combined demand function QS = 35 - 7P. Inverted, this becomes P = 5 - Q/7, representing society's willingness to pay for fireworks.
Step-by-step explanation:
The social marginal benefit of firework consumption is the willingness of society to pay for an additional unit of fireworks. To find this, we horizontally sum Barton's and Jay's individual demand functions.
Barton's demand for fireworks is given by QB = 25 − 5P, and Jay's demand is QJ = 10 − 2P. To determine the combined demand, we add the quantities at each price, which results in QS = QB + QJ.
By substituting the individual demand equations into the combined demand, we get QS = (25 − 5P) + (10 − 2P) = 35 − 7P. Inverting this equation to solve for P as a function of Q, we find P = 5 − QS/7. This represents the price (willingness to pay) associated with each quantity Q of fireworks demanded by society.