If (3x+31)/0.4=100, that is 5x+7=how much.
如果(3x+31)/0.4=100，即5x+7=多少．
<gadget id="calculator">31 / 0.4</gadget>
<output>77.5</output>

<gadget id="calculator">100 - 77.5</gadget>
<output>22.5</output>

<gadget id="calculator">3 / 0.4</gadget>
<output>7.5</output>

<gadget id="calculator">22.5 / 7.5</gadget>
<output>3</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 + 7</gadget>
<output>22</output>

<result>22</result>