The ratio of the base angle to the apex angle of an isosceles triangle is 4:1, what is the base angle?
等腰三角形底角度数与顶角度数的比是4：1，它的底角是多少度．
<gadget id="calculator">4 / 4 / 1</gadget>
<output>1</output>

<gadget id="calculator">4 + 4 + 1</gadget>
<output>9</output>

<gadget id="calculator">180 / 9</gadget>
<output>20</output>

<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<result>80</result>