The sum of A and B is 19.5. After taking out (1/6) of A's number and giving it to B's number, B's number is (6/7) of A's number. What is the original number of B's number?
甲、乙两数的和是19.5，取出甲数的(1/6)给乙数后，乙数是甲数的(6/7)，乙数原来是多少．
<gadget id="calculator">6 / 7</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">19.5 * (6/7)</gadget>
<output>16.714286</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">19.5 * (1/6) * (6/7)</gadget>
<output>2.785714</output>

<gadget id="calculator">19.5 * (1/6)</gadget>
<output>3.25</output>

<gadget id="calculator">16.714286 - 2.785714 - 3.25</gadget>
<output>10.678572</output>

<gadget id="calculator">(1/6) * (6/7)</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (1/7) - (1/6)</gadget>
<output>29/42 = around 0.690476</output>

<gadget id="calculator">(6/7) + (29/42)</gadget>
<output>65/42 = around 1.547619</output>

<gadget id="calculator">10.678572 / (65/42)</gadget>
<output>6.9</output>

<result>6.9</result>