A customer bought a product at the shop. However, the shopkeeper increased the price of the product by 20% so that the customer could not buy the required amount of the product. The customer managed to buy only 80% of the required amount. What is the difference in the amount of money that the customer paid for the second purchase compared to the first purchase?  Choose the most appropriate option.
A) 10 %
B) 8 %
C) 6 %
D) 4 %
E) 2 %

Rationale: "let x be the amount of money paid for the first purchase . the second time , the customer paid 0.8 ( 1.2 x ) = 0.96 x . the difference is 4 % . the answer is d ."
Answer: D