After a circle is enlarged by 3:1, its radius is 12 cm. What is the radius of the original circle in cm?
一个圆按3：1放大后，半径是12cm，原来的圆的半径是多少cm．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">12 * (1/3)</gadget>
<output>4</output>

<result>4</result>