batch of parts, A alone takes 10 hours to complete, B makes 20 parts per hour, and the two work together in 6 hours. How many parts are there in this batch?
一批零件，甲单独做要10小时完成，乙每小时做20个零件，两人合做6小时完成．这批零件有多少个？
<gadget id="calculator">10 + 20</gadget>
<output>30</output>

<gadget id="calculator">30 * 6</gadget>
<output>180</output>

<result>180</result>