20 bananas, 6 in each basket, how many bananas can be removed, and 3 baskets can be filled exactly.
20个香蕉，每篮装6个，拿掉多少个，就可以正好装3个篮子了．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">20 - 18</gadget>
<output>2</output>

<result>2</result>