It takes 5 minutes for A to make one part, and 9 minutes for B to make one part. If two people work together to make 84 parts at the same time, how many parts will A make when they are finished?
甲做一个零件要5分钟，乙做一个零件要9分钟，如果两人同时合做84个零件，完成时甲做了多少零件．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/5) + (1/9)</gadget>
<output>14/45 = around 0.311111</output>

<gadget id="calculator">84 / (14/45)</gadget>
<output>270</output>

<gadget id="calculator">270 / 5</gadget>
<output>54</output>

<result>54</result>