The sum of the upper and lower bases of a right-angled trapezoid is 20 cm, its circumference is 35 cm, and the length of one waist is twice the length of the other. What is the length of the shorter waist?
一个直角梯形的上底与下底的和是20厘米，它的周长是35厘米，一条腰长是另一条腰长的2倍，短的这条腰长是多少．
<gadget id="calculator">35 - 20</gadget>
<output>15</output>

<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<result>5</result>