The charging standards for public telephones are as follows: 0.22 yuan for less than 3 minutes, and 0.10 yuan per minute for more than 3 minutes. Xiao Ming once spent 0.27 yuan on a public phone, how many minutes did he call?
公用电话的收费标准如下：在3分钟以内收费0.22元，超过3分钟后，每分钟收0.10元．小明有一次在公用电话用了0.27元，他打了多少分钟电话．
<gadget id="calculator">0.27 - 0.22</gadget>
<output>0.05</output>

<gadget id="calculator">0.05 / 0.1</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 + 3</gadget>
<output>3.5</output>

<result>3.5</result>