The starting price of a taxi in a city is 7 yuan (within 3 kilometers), and the average price per kilometer is 2.4 yuan for more than 3 kilometers. Lu Wei paid a total of 17.8 yuan for the bus from his home to Xinhua Bookstore. May I ask how many kilometers it is from his home to Xinhua Bookstore?
某城市出租车起步价为7元(3千米以内)，超过3千米，平均每千米为2.4元．陆伟从他家到新华书店共付车费17.8元，请问他从家到新华书店有多少千米？
<gadget id="calculator">17.8 - 7</gadget>
<output>10.8</output>

<gadget id="calculator">10.8 / 2.4</gadget>
<output>4.5</output>

<gadget id="calculator">4.5 + 3</gadget>
<output>7.5</output>

<result>7.5</result>