Some new billboards were installed every 4 meters on one side of the road, but there were no billboards because one end was a bridge pier. Xiaolan counted from beginning to end, and there were 42 billboards in total. How many meters is this road?
公路的一边每隔4米新装了一些广告牌，因为一头是桥墩所以没有装，小兰从头到尾数了一下，一共42块公告牌．这条公路长多少米？
<gadget id="calculator">4 * 42</gadget>
<output>168</output>

<result>168</result>