The Shanghai-Jiajia Expressway is 15.9 kilometers long, and the roads entering the city at both ends are 4.6 kilometers long. How long is this highway in kilometers?
沪嘉高速公路长15.9千米，两端的入城道路各长4.6千米，这条公路全长多少千米？
<gadget id="calculator">4.6 * 2</gadget>
<output>9.2</output>

<gadget id="calculator">9.2 + 15.9</gadget>
<output>25.1</output>

<result>25.1</result>