It is known that the sum of the apex angle and a base angle of an isosceles triangle is 140°, then what is the apex angle of this triangle.
已知一个等腰三角形的顶角与一个底角的和是140°，那么这个三角形的顶角是多少．
<gadget id="calculator">180 - 140</gadget>
<output>40</output>

<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<gadget id="calculator">180 - 80</gadget>
<output>100</output>

<result>100</result>