Parking in a parking lot costs at least 8 yuan once. If you park for more than 3 hours, you will have to pay 2.5 yuan for each additional hour. The car paid 18 yuan when it left the parking lot. How long has the car been parked?
在一个停车场停车一次至少要交费8元．如果停车超过3小时，每多停1小时要多交2.5元．这辆汽车在离开停车场时交了18元，这辆汽车停了多长时间？
<gadget id="calculator">18 - 8</gadget>
<output>10</output>

<gadget id="calculator">10 / 2.5</gadget>
<output>4</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<result>7</result>