Tie two wine bottles in a circle with a rope. The outer diameter of the wine bottle is 6 cm, and a 15 cm rope is needed for the knot. About how long will this rope be?
用绳子将两个酒瓶捆一圈，酒瓶的外直径是6厘米，打结处需要15厘米的绳子．问这根绳子大约需要多长？
<gadget id="calculator">3.14 * 6</gadget>
<output>18.84</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">18.84 + 12 + 15</gadget>
<output>45.84</output>

<result>45.84</result>