Parking in a parking lot costs at least 8 yuan once. If you park for more than 3 hours, you will have to pay an additional 2.5 yuan for each additional hour of parking. A car paid 23 yuan when it left. 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小时车要多交2.5元．一辆汽车在离开时交了23元，这辆车停了多长时间？
<gadget id="calculator">23 - 8</gadget>
<output>15</output>

<gadget id="calculator">15 / 2.5</gadget>
<output>6</output>

<gadget id="calculator">6 + 3</gadget>
<output>9</output>

<result>9</result>