21 trees are planted on one side of a road, and both ends are planted. There is 5 meters between every two trees. How many meters is the road in total?
在一条马路的一边种上21棵树，且两头都种，每两棵树之间有5米，这条马路一共有多少米．
<gadget id="calculator">21 - 1</gadget>
<output>20</output>

<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<result>100</result>