The sum of A and B is 108, and the ratio of A and B is 4:5. What is the difference between B and A?
甲、乙两数的和是108，甲数与乙数的比是4：5，则乙数与甲数的差是多少．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">108 * (5/9)</gadget>
<output>60</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">108 * (4/9)</gadget>
<output>48</output>

<gadget id="calculator">60 - 48</gadget>
<output>12</output>

<result>12</result>