Local calls: 0.2 yuan for the first 3 minutes, and 0.1 yuan per minute thereafter; long-distance calls: 0.1 yuan for every 10 seconds. Xiao Ming first made a local call to his father, which took 6 minutes, and then made a long-distance call, which cost a total of 2.1 yuan. How long is the long-distance call?
市内电话：前3分钟付0.2元，以后每分钟付0.1元；长途电话：每10秒钟付0.1元．小明先打了一个市内电话给爸爸，用了6分钟，随后又打了一个长途电话，总共花了2.1元钱，长途电话的通话时间是多少？
<gadget id="calculator">6 - 3</gadget>
<output>3</output>

<gadget id="calculator">3 * 0.1</gadget>
<output>0.3</output>

<gadget id="calculator">0.2 + 0.3</gadget>
<output>0.5</output>

<gadget id="calculator">2.1 - 0.5</gadget>
<output>1.6</output>

<gadget id="calculator">1.6 / 0.1</gadget>
<output>16</output>

<gadget id="calculator">16 * 10</gadget>
<output>160</output>

<result>160</result>