The first phase of the Nanjing Metro project is divided into two parts: the elevated line and the underground line. The underground line is 1.6 times as long as the elevated line, and the length of the underground line is 3.9 kilometers longer than the elevated line. How many kilometers is the whole line of the first phase of the project?
南京地铁一期工程分高架线和地下线两部分，其中地下线是高架线的1.6倍，地下线的长度比高架线长3.9千米．一期工程全线长多少千米？
<gadget id="calculator">1.6 - 1</gadget>
<output>0.6</output>

<gadget id="calculator">3.9 / 0.6</gadget>
<output>6.5</output>

<gadget id="calculator">6.5 * 1.6</gadget>
<output>10.4</output>

<gadget id="calculator">6.5 + 10.4</gadget>
<output>16.9</output>

<result>16.9</result>