The ratio of A and B is 1:4. If A subtracts 3, the ratio of A and B is 1:6. What is the original number of A?
甲、乙两数的比是1：4，如果甲减去3后，甲与乙的比是1：6，甲数原来是多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) - (1/6)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">3 / (1/12)</gadget>
<output>36</output>

<gadget id="calculator">36 * (1/4)</gadget>
<output>9</output>

<result>9</result>