There is an isosceles triangle, the sum of its apex and a base angle is 150°, what is its apex angle?
有一个等腰三角形，它的顶角与一个底角的和是150°，它的顶角是多少．
<gadget id="calculator">180 - 150</gadget>
<output>30</output>

<gadget id="calculator">150 - 30</gadget>
<output>120</output>

<result>120</result>