Harder Corporation uses the perpetual inventory method. On March 1, it purchased $30,000 of inventory, terms 2/10, n/30. On March 3, Harder returned goods that cost $3,000. On March 9, Harder paid the supplier. On March 9, Harder should credit
a. purchase discounts for $600.
b. inventory for $600.
c. purchase discounts for $540.
d. inventory for $540.