A trapezoidal vegetable field has an upper base of 20 meters and a lower base of 40 meters, covering an area of 600 square meters. What is the distance between two parallel sides of this vegetable field in meters?
一块梯形菜地，上底20米，下底40米，占地面积为600平方米，这块菜地两条平行边间的距离为多少米．
<gadget id="calculator">20 + 40</gadget>
<output>60</output>

<gadget id="calculator">2 / 60</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">600 * (1/30)</gadget>
<output>20</output>

<result>20</result>