There are 81 electric poles on one side of a road from the beginning to the end, and the distance between each two adjacent poles is 45 meters. Due to the widening of the road, it is planned to adjust the distance between each two adjacent poles to be 60 meters from the beginning to the end. How many wires need to be reduced in this way? pole.
某马路的一侧从头到尾原有电线杆81根，每相邻的两根相距45米，因扩宽马路，计划从头到尾调整成每相邻两根相距60米，这样需要减少多少根电线杆．
<gadget id="calculator">81 - 1</gadget>
<output>80</output>

<gadget id="calculator">80 * 45</gadget>
<output>3_600</output>

<gadget id="calculator">3_600 / 60</gadget>
<output>60</output>

<gadget id="calculator">60 + 1</gadget>
<output>61</output>

<gadget id="calculator">81 - 61</gadget>
<output>20</output>

<result>20</result>