Hugh Warner is a very cautious businessman. His supplier offers trade credit terms of 3/14, net 80.

Mr. Hugh Warner is a very cautious businessman. His supplier offers trade credit terms of 3/14, net 80. Mr. Warner never takes the discount offered, but he pays his suppliers in 70 days rather than the 80 days allowed so he is sure the payments are never late.  

What is Mr. Warner's cost of not taking the cash discount?