Three Brothers Pizza recently decided to raise its regular price on medium pizzas from $8 to $12 following increases in the costs of labor and materials. Unfortunately, sales dropped sharply from 8,100 to 4,200 pizzas per month. In an effort to regain lost sales, Three Brothers ran a coupon promotion featuring $5 off the new regular price. Coupon printing and distribution costs totaled $100, and caused only a modest increase in the typical advertising budget of $2,400 per month. The promotion was judged a success as it proved highly popular with consumers. In the period prior to expiration, coupons were used on 40% of all purchases and monthly sales rose to 8000 pizzas.

A.	Calculate the arc price elasticity implied by the initial response to Three Brother's price increase.
B.	Calculate the effective price reduction resulting from the coupon promotion.
C.	In light of this price reduction, and assuming no change in the price elasticity of demand, calculate Three Brother's arc advertising elasticity.
D.	Why might the true arc advertising elasticity differ from that calculated in Part C? Explain your reasoning carefully.