piece of steel is 4.2 meters long, 3/7 of the full length is used for the first time, and 1.2 meters is used for the second time, how many meters are left?
一根钢材长4.2米，第一次用去全长的(3/7)，第二次用去1.2米，还剩多少米？
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">4.2 * (3/7)</gadget>
<output>1.8</output>

<gadget id="calculator">1.8 + 1.2</gadget>
<output>3</output>

<gadget id="calculator">4.2 - 3</gadget>
<output>1.2</output>

<result>1.2</result>