There are 90 books on shelf A, and 30 books on shelf B. After taking the same number of books from both shelves A and B, the number of books left on shelf A is 4 times that of B. How many books are taken from each of the two shelves? Book?
甲书架有90本书，乙书架有30本书，从甲、乙两个书架拿走相同的本数后，甲书架剩下的本数是乙的4倍，从甲乙两个书架各拿走多少本书？
<gadget id="calculator">30 * 4</gadget>
<output>120</output>

<gadget id="calculator">120 - 90</gadget>
<output>30</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<result>10</result>