A ship departs from Port A at 7:30 and arrives at Port B at 5:30 p.m., sailing an average of 30 kilometers per hour. How many kilometers is the waterway between these two ports?
一艘船7时30分从甲港出发，下午5时30分到达乙港，平均每小时航行30千米，这两个港口之间的水路长多少千米．
<gadget id="calculator">17.5 - 7.5</gadget>
<output>10</output>

<gadget id="calculator">30 * 10</gadget>
<output>300</output>

<result>300</result>