Some exercise books are divided among A, B, and C, A (1/7) is allocated to B (1/4), and the amount distributed to C is twice the difference between the amounts distributed to A and B. At this time, there are 11 exercise books left. How many exercise books does A get? (Hint: You can draw a graph for analysis)
一些练习本分给甲、乙、丙三个人，分给甲(1/7)，分给乙(1/4)，分给丙的数量是分给甲、乙二人数量差的2倍，这时还剩11本练习本．甲分到几本练习本？(提示：可画图分析)
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</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 - (1/7) - (1/4) - (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>