A steamship sails from port A to port B, travels 20 kilometers per hour downstream, and spends 60 hours upstream on the way back. It is known that the current of this channel is 4 kilometers per hour, how many kilometers is the distance from port A to port B?
一只轮船从A港开往B港，顺流而下每小时行20千米，返回时逆流而上用了60小时．已知这段航道的水流是每小时4千米，求A港到B港相距多少千米？
<gadget id="calculator">20 - 6</gadget>
<output>14</output>

<gadget id="calculator">14 * 60</gadget>
<output>840</output>

<result>840</result>