The sum of the interior angles of a triangle is 180°. Calculate the sum of the interior angles of a pentagon.
三角形的内角和是180°，算一算，五边形的内角和是多少度．
<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">180 * 3</gadget>
<output>540</output>

<result>540</result>