The starting price of a taxi in Xi’an is 7 yuan (within 3 kilometers), and 2.4 yuan per kilometer for more than 3 kilometers. Teacher Wang paid 17.8 yuan for the taxi from home to school. How far is it from his home to school?
西安市的出租车起步价是7元(3千米以内)，超过3千米每千米为2.4元，王老师从家到学校共付车费17.8元，他家到学校多少千米？
<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">3 + 4.5</gadget>
<output>7.5</output>

<result>7.5</result>