The school distributes 72 extra-curricular reading materials to A, B, and two classes at a ratio of 5:4. How many more books are there in Class A than in Class B?
学校把72本课外读物按5：4分配给A、B、两个班，A班比B班多分多少本．
<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">72 * (5/9)</gadget>
<output>40</output>

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

<gadget id="calculator">72 * (4/9)</gadget>
<output>32</output>

<gadget id="calculator">40 - 32</gadget>
<output>8</output>

<result>8</result>