Two ports, A and B, are 400 kilometers apart. A ship goes down the river from port A and can reach port B in 20 hours. It is known that the speed of the boat going with the current is twice the speed of the boat against the current. Once, the ship encountered an emergency on the way from port A to port B. After sailing in the opposite direction for a certain distance, it turned around and sailed to port B. As a result, it was 9 hours late. How many kilometers did the ship travel more than normal on this voyage?
甲乙两个港口相距400千米，一艘轮船从甲港顺流而下，20小时可到达乙港．已知顺水船速是逆水船速的2倍．有一次，这艘船在由甲港驶向乙港途中遇到突发事件，反向航行一段距离后，再掉头驶向乙港，结果晚到9个小时．轮船的这次航行比正常情况多行驶了多少千米．
<gadget id="calculator">400 / 20</gadget>
<output>20</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

<gadget id="calculator">20 * 3 * 2</gadget>
<output>120</output>

<result>120</result>