A circular fish pond with a radius of 50 meters is planned to pave a 10-meter circular road around it, and use 20 kilograms of concrete per square meter. How many kilograms of concrete are needed to pave a road?
一个半径50米的圆形鱼池，计划在它的周围围铺一条10米的环形马路，每平方用混泥土20千克．铺一条马路一共需要多少千克的混泥土？
<gadget id="calculator">50 + 10</gadget>
<output>60</output>

<gadget id="calculator">60 ** 2</gadget>
<output>3_600</output>

<gadget id="calculator">50 ** 2</gadget>
<output>2_500</output>

<gadget id="calculator">3_600 - 2_500</gadget>
<output>1_100</output>

<gadget id="calculator">3.14 * 1_100 * 20</gadget>
<output>69_080</output>

<result>69_080</result>