There are many machine parts of the same kind in the box, 3/5 of them are first-class products, 25% are second-class products, and the remaining 51 are third-class products. How many first-class parts are there in the box?
箱子里放了许多同一种机器零件，其中五分之三是一等品，25%是二等品，其余51个是三等品，箱子中的零件一等品有多少个．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (3/5) - (1/4)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">51 / (3/20)</gadget>
<output>340</output>

<gadget id="calculator">340 * (3/5)</gadget>
<output>204</output>

<result>204</result>