Given that one interior angle of a quadrilateral is 80°, the second interior angle is half of the first interior angle, and the third interior angle is three times the second interior angle, find the fourth interior angle.
已知一个四边形的一个内角是80°，第二个内角是第一个内角的一半，第三个内角是第二个内角的3倍，求第四个内角．
<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">360 - 80 - 40 - 120</gadget>
<output>120</output>

<result>120</result>