1.28x+0.28*(45-x)=27.6, x=how much.
1.28x+0.28*(45-x)=27.6，x=多少．
<gadget id="calculator">0.28 * 45</gadget>
<output>12.6</output>

<gadget id="calculator">27.6 - 12.6</gadget>
<output>15</output>

<gadget id="calculator">1.28 - 0.28</gadget>
<output>1</output>

<gadget id="calculator">15 / 1</gadget>
<output>15</output>

<result>15</result>