For an isosceles triangle roof, the top angle is known to be 140°, and one base angle = how many degrees.
一个等腰三角形的屋顶，已知顶角是140°，一个底角=多少度．
<gadget id="calculator">180 - 140</gadget>
<output>40</output>

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

<result>20</result>