Such as 5b=9a, b=4.5, then a=how much.
如5b=9a，b=4.5，那么a=多少．
<gadget id="calculator">4.5 * 5</gadget>
<output>22.5</output>

<gadget id="calculator">22.5 / 9</gadget>
<output>2.5</output>

<result>2.5</result>