Two ships sail oppositely from two piers at the same time. Ship A travels 48 nautical miles per hour, and boat B travels 52 nautical miles per hour. After 8.4 hours, the two ships meet. What is the distance between the two piers?
两船同时从两个码头相对开出，甲船每小时行48海里，乙船每小时行52海里，8.4小时后，两船相遇，两个码头间的距离是多少海里？
<gadget id="calculator">48 + 52</gadget>
<output>100</output>

<gadget id="calculator">100 * 8.4</gadget>
<output>840</output>

<result>840</result>