Need help on this follow-up question

3 Kersee Company on June 15 sells merchandise on account to Eng Co. for $1,000, terms 2/10, n/30. On June 20, Eng Co. returns merchandise worth $300 to Kersee Company. On June 24, payment is received from Eng Co. for the balance due. What is the amount of cash received?

(a) $700.

(b) $680.

(c) $686.

(d) None of the above.

question 3 refers to "2/10, net 30".Can you tell us what the APR of this discount would be?