Four people, A, B, C, and D, solve problems. A solves 1/3 of the total number of problems, and B solves 1/5 of the total number of problems. The ratio of C and D to solve problems is 4:3. If A solves more problems than B 6 questions, how many questions did Ding solve?
甲乙丙丁四人解题，甲解的题占总数的(1/3)，乙解的题占总数的(1/5)，而丙丁解题之比是4：3，如果甲比乙多解6道题，丁的解题数多少．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) - (1/5)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">6 / (2/15)</gadget>
<output>45</output>

<gadget id="calculator">1 - (1/3) - (1/5)</gadget>
<output>7/15 = around 0.466667</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">45 * (7/15) * (3/7)</gadget>
<output>9</output>

<result>9</result>