A and B work together to clean up the snow on the 400-meter circular runway. They walk from the same place with their backs at the same time to clean up separately. At first, A cleans up faster than B. Later, B spends 10 minutes to change tools and come back to continue. Cleaning, but the work efficiency has doubled compared to the original. As a result, counting from the time when A and B started cleaning, after 1 hour, the snow clearing work was completed, and the runway they cleared was the same length. How many minutes did B work after changing the tool?
甲、乙两人合作清理400米环形跑道上的积雪，两人同时从同一地点背向而行各自进行清理，最初甲清理的速度比乙快，后来乙用10分钟去调换工具，回来继续清理，但工作效率比原来提高了一倍，结果从甲、乙开始清理时算起，经过1小时，就完成了清理积雪工作，并且两人清理的跑道一样长．问乙换工具后又工作了多少分钟？
<gadget id="calculator">2.5 * 10</gadget>
<output>25</output>

<gadget id="calculator">2.5 * 60</gadget>
<output>150</output>

<gadget id="calculator">200 - 150</gadget>
<output>50</output>

<gadget id="calculator">25 + 50</gadget>
<output>75</output>

<gadget id="calculator">2 * 2.5</gadget>
<output>5</output>

<gadget id="calculator">5 - 2.5</gadget>
<output>2.5</output>

<gadget id="calculator">75 / 2.5</gadget>
<output>30</output>

<result>30</result>