When X=how much, the value of 6X+4.5X is equal to 21.
当X=多少时，6X+4.5X的值等于21．
<gadget id="calculator">6 + 4.5</gadget>
<output>10.5</output>

<gadget id="calculator">21 / 10.5</gadget>
<output>2</output>

<result>2</result>