A steamship sails from Pier A to Pier B, travels 15 kilometers per hour against the current, and travels downstream for 18 hours when returning. It is known that the water flow in this channel is 3 kilometers per hour. How many kilometers is the waterway between A and B?
一只轮船从甲码头开往乙码头，逆流每小时行15千米，返回时顺流而下用了18小时．已知这段航道的水流是每小时3千米，求甲、乙两个码头间水路长多少千米？
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">15 + 6</gadget>
<output>21</output>

<gadget id="calculator">21 * 18</gadget>
<output>378</output>

<result>378</result>