Two ships, A and B, sail from Shanghai to Wuhan at the same time. Ship A travels 24 kilometers per hour. After 8.5 hours, ship A surpasses ship B by 51 kilometers. How many kilometers does the boat travel per hour?
甲乙两艘轮船同时从上海开往武汉，甲船每小时行24千米，经过8.5小时甲船超过乙船51千米．乙船每小时行多少千米？
<gadget id="calculator">24 * 8.5</gadget>
<output>204</output>

<gadget id="calculator">204 - 51</gadget>
<output>153</output>

<gadget id="calculator">153 / 8.5</gadget>
<output>18</output>

<result>18</result>