Given a triangular frame with a side length of 70 meters and a base length of 30 meters, what is the waist length in meters?
有一个边长是70米的三角形框架，底边长30米，腰长是多少米？
<gadget id="calculator">70 - 30</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>