If 0.39x+14.2=33.7, then 0.8x-17.9=how much.
如果0.39x+14.2=33.7，那么0.8x-17.9=多少．
<gadget id="calculator">33.7 - 14.2</gadget>
<output>19.5</output>

<gadget id="calculator">19.5 / 0.39</gadget>
<output>50</output>

<gadget id="calculator">0.8 * 50</gadget>
<output>40</output>

<gadget id="calculator">40 - 17.9</gadget>
<output>22.1</output>

<result>22.1</result>