The shape of the runway is a rectangle in the middle and semicircles on both sides. The side length of the rectangle is 9 cm. Find the perimeter of the runway.
跑道形状，中间为矩形，两边是半圆形，矩形边长是9厘米，求跑道的周长．
<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<gadget id="calculator">28.26 + 18</gadget>
<output>46.26</output>

<result>46.26</result>