The school purchased a new batch of books and distributed them to the fourth, fifth and sixth grades according to the ratio of 4:5:6. It is known that the fourth grade is 40 books less than the sixth grade. How many books are allocated to the fifth grade?
学校新购进一批图书，分别按4：5：6的比例分给四、五、六三个年级，已知四年级比六年级少40本，五年级分到图书多少本？
<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<result>100</result>