In a parking lot, it is stipulated that the parking fee is 7 yuan within 2 hours, and 3.5 yuan per hour for the part exceeding 2 hours. How much is the parking fee for 5 hours? Uncle Liu paid 21 yuan when he left. How long did he park in the parking lot?
一停车场内规定2小时内收7元停车费，超过2小时的部分每小时收3.5元，停5小时收费多少元？刘叔叔离开时交了21元，他在停车场停了多长时间？
<gadget id="calculator">14 / 3.5</gadget>
<output>4</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<result>6</result>