Local call charges: 0.2 yuan for the first 3 minutes, 0.1 yuan per minute thereafter; long-distance call charges: 0.1 yuan per 10 seconds. Ding Ding 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 many seconds did it take for Ding Ding to make a long-distance call?
市内电话收费：前3分钟0.2元，以后每分钟0.1元；长途电话收费：每10秒钟0.1元．丁丁先打了一个市内电话给爸爸，用了6分钟，然后又打了一个长途电话，共花了2.1元的电话费，丁丁打长途电话的时间是多少秒？
<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>