Xiaohong bought a red scarf in an isosceles triangle. One of its base angles is 20°. What is its top angle?
小红买了一条等腰三角形的红领巾，它的一个底角是20°，它的顶角是多少度？
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">180 - 40</gadget>
<output>140</output>

<result>140</result>