Distribute a batch of pencils to A, B, and C, distribute to A (1/7), and distribute to B (1/4). The amount distributed to C is 2 of the difference between the amounts distributed to A and B. times, and there are 11 pencils left at this time, how many pencils will A get.
把一批铅笔分给甲、乙、丙三人，分给甲(1/7)，分给乙(1/4)，分给丙的数量是分给甲、乙两人数量的差的2倍，这时还剩下11支铅笔，则甲分到多少支．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(1/4) - (1/7)</gadget>
<output>3/28 = around 0.107143</output>

<gadget id="calculator">(3/28) * 2</gadget>
<output>3/14 = around 0.214286</output>

<gadget id="calculator">1 - (1/4) - (1/7) - (3/14)</gadget>
<output>11/28 = around 0.392857</output>

<gadget id="calculator">11 / (11/28)</gadget>
<output>28</output>

<gadget id="calculator">28 * (1/7)</gadget>
<output>4</output>

<result>4</result>