There is an isosceles triangle, its top angle is 30 degrees, what is its base angle in degrees?
有一个等腰三角形，它的顶角是30度，它的一个底角是多少度．
<gadget id="calculator">180 - 30</gadget>
<output>150</output>

<gadget id="calculator">150 / 2</gadget>
<output>75</output>

<result>75</result>