The sixth grade students of East Changjiang Road Elementary School are learning Mathematics Olympiad. In the first term (2/7) they have learned all the courses. After the second term (1/3) there are 6 more lectures left, and finally there are 14 lectures left. study. How many Olympiad courses do they have to learn in total? (Backward method to solve the problem)
长江东路小学六年级的学生学习奥数课程，第一期学了全部课程的(2/7)，第二期学后余下的(1/3)还多6讲，最后还剩下14讲没学．他们一共要学多少讲的奥数课程？(倒推法解题)
<gadget id="calculator">14 + 6</gadget>
<output>20</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/7)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">20 / (2/3) / (5/7)</gadget>
<output>42</output>

<result>42</result>