Please give good explination. Thank you!

Assume the perpetual inventory method is used. 1) Marathon Company purchased merchandise inventory that cost $8,000 under terms of 2/10, n/30 and FOB shipping point. 2) Marathon paid freight cost of $500 on the merchandise. 3) Marathon made payment to the supplier within the discount period. 4) All of the goods were sold to customers on account for $12,000, The Gross margin from these transactions is: O $3,060 0 $4,160 O $3,660 O $4,000