If the vertex angle of an isosceles triangle is 2.5 times the base angle, what is the vertex angle of the isosceles triangle?
一个等腰三角形的顶角是底角的2.5倍，则等腰三角形的顶角是多少度．
<gadget id="calculator">2.5 + 1 + 1</gadget>
<output>4.5</output>

<gadget id="calculator">180 / 4.5</gadget>
<output>40</output>

<gadget id="calculator">2.5 * 40</gadget>
<output>100</output>

<result>100</result>