parking lot requires 10 yuan for parking within 2 hours, and 2.1 yuan per half hour for more than 2 hours (less than half an hour is calculated as half an hour). Dad parks in this parking lot at 4:25, how much is the total parking fee?
一停车场规定停车2小时内收10元停车费，超过2小时，超过的时间每半小时收费2.1元(不足半小时按半小时计算)．爸爸在这个停车场停车4时25分，一共要付停车费多少元？
<gadget id="calculator">2.1 * 5</gadget>
<output>10.5</output>

<gadget id="calculator">10 + 10.5</gadget>
<output>20.5</output>

<result>20.5</result>