Three good friends all participated in the painting competition. The average score of the first and second place is 17 points, and the average score of the second and third place is 20 points. What is the difference between the scores of the third place and the first place? ．
有三位好朋友都参加了绘画比赛，第一位与第二位的平均成绩是17分，第二位与第三位的平均成绩是20分，第三位和第一位的成绩相差多少分．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">17 * 2</gadget>
<output>34</output>

<gadget id="calculator">40 - 34</gadget>
<output>6</output>

<result>6</result>