Uncle workers want to install street lamps on one side of the road, one every 4 meters from the beginning, a total of 30 are installed, how long is this road in meters?
工人叔叔要在马路的一侧安装路灯，从头开始每隔4米安一个，共安装了30个，这条路长多少米．
<gadget id="calculator">30 - 1</gadget>
<output>29</output>

<gadget id="calculator">29 * 4</gadget>
<output>116</output>

<result>116</result>