A bridge is 141 meters long. There are 18 billboards installed on both sides of the bridge. Each billboard is 2 meters long. The billboards near both ends of the bridge are 10 meters away from the bridge head.
一座桥长141米，在桥两侧各安装18块广告牌，每块广告牌横长2米，靠近桥两端的广告牌离桥头10米，相邻两块广告牌相隔多少米？
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">141 - 20</gadget>
<output>121</output>

<gadget id="calculator">2 * 18</gadget>
<output>36</output>

<gadget id="calculator">121 - 36</gadget>
<output>85</output>

<gadget id="calculator">85 / 17</gadget>
<output>5</output>

<result>5</result>