The sum of A and B is 28, and the ratio of A to B is 3:4. What is the difference between the two numbers A and B?
甲乙两数的和是28，甲数与乙数的比是3：4．甲乙两数的差是多少．
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

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

<gadget id="calculator">28 * (3/7)</gadget>
<output>12</output>

<gadget id="calculator">28 - 12</gadget>
<output>16</output>

<gadget id="calculator">16 - 12</gadget>
<output>4</output>

<result>4</result>