For fixed-line calls in a certain city, the charge is 0.15 yuan per minute for the first 3 minutes, and 0.12 yuan per minute for more than 3 minutes (less than 1 minute is calculated as 1 minute). Obviously, it takes 6 minutes to make a call to Dad. How much does he charge for this call?
某城市打固定电话，每次前3分钟按每分钟0.15元收费，超过3分钟每分钟收费0.12元(不足1分钟按1分钟计算)．明明给爸爸一次通话是6分钟，他这一次通话的费用是多少元？
<gadget id="calculator">6 - 3</gadget>
<output>3</output>

<gadget id="calculator">3 * 0.12</gadget>
<output>0.36</output>

<gadget id="calculator">0.36 + 0.15</gadget>
<output>0.51</output>

<result>0.51</result>