A cumulative revolving documentary credit was issued in December for an original amount of USD 25,000, valid for six months. The documentary credit has revolved three times as follows: January : USD 25,000 February: USD 25,000 March : USD 25,000 The documentary credit has been drawn and paid as follows: January : USD 20,000 February: USD 20,000 March: USD 15,000 What is the liability of the issuing bank after the March drawing?