A street is 20 meters long. From one end of the road, trees are planted on both sides of the road every 4 meters. How many trees are there in total?
一条大街长20米，从路的一端起，每隔4米在路的两侧各种一棵树，则共有多少棵树．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>