There is an isosceles trapezoid, the upper base is 10 cm long, the lower base is 20 cm long, and the two base angles are 60°. Divide the two waists into 40 parts on average, and then connect the corresponding equal points. The total length of the connecting line how many?
有一个等腰梯形，上底长10厘米，下底长20厘米，两个底角是60°，把两腰各平均分成40份，然后把对应的等分点连接起来，其连线的总长是多少？
<gadget id="calculator">10 + 20</gadget>
<output>30</output>

<gadget id="calculator">40 - 1</gadget>
<output>39</output>

<gadget id="calculator">39 / 2</gadget>
<output>39/2 = around 19.5</output>

<gadget id="calculator">30 * (39/2)</gadget>
<output>585</output>

<result>585</result>