The number 1.6 less than twice X is 8.4, then X=how much.
比X的2倍少1.6的数是8.4，则X=多少．
<gadget id="calculator">6.4 + 1.6</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<result>4</result>