求解这道ACCA关于弹性的计算题。要解题步骤！

求解这道ACCA关于弹性的计算题。要解题步骤！

PED = %change in quantity / %change in price
% change in price is $4 / $20 = 20%

What is change in quantity?

Original sales = 100 shirts x $20 = $2,000
New sales = $2,000 x 114% = $2,280
New quantity = $2,280 / $24 = 95 shirts
Change in quantity = 5 shirts / 100  shirts = 5%

PED = 5% / 20% = 0.25 (Answer B)

I guess.