The No. 1 subway project in a certain city is divided into two parts: the underground line and the elevated line. Among them, the length of the underground line is about 12.35 kilometers, and the length of the underground line is 2.1 times that of the elevated line, which is 0.8 kilometers longer. How many kilometers is the whole line of No. 1 subway project?
某市一号地铁工程分地下线和高架线两部分．其中地下线约长12.35千米，地下线的长度是高架线的2.1倍还多0.8千米．一号地铁工程全线长多少千米？
<gadget id="calculator">12.35 - 0.8</gadget>
<output>11.55</output>

<gadget id="calculator">11.55 / 2.1</gadget>
<output>5.5</output>

<gadget id="calculator">5.5 + 12.35</gadget>
<output>17.85</output>

<result>17.85</result>