Plant a tree every 4 meters on both sides of a 120-meter-long road (both ends are planted), how many trees should be planted in total?
在一条长120米的路两旁每隔4米栽一棵树(两端都栽)，一共要栽多少棵．
<gadget id="calculator">120 / 4</gadget>
<output>30</output>

<gadget id="calculator">30 + 1</gadget>
<output>31</output>

<gadget id="calculator">31 * 2</gadget>
<output>62</output>

<result>62</result>