There are two bookshelves, A and B. The books on shelf A are 1.5 times the number of books on shelf B. If you take 20 books from shelf B and put them into shelf A, then A is 4 times the number of books on shelf B. How many books are there on shelf A? (solution by equation)
有甲乙两个书架，甲书架的书是乙书架书的1.5倍，如果从乙书架拿20本放入甲书架，这时甲是乙的4倍，原来甲书架有多少本书？(用方程解)
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">20 + 80</gadget>
<output>100</output>

<gadget id="calculator">4 - 1.5</gadget>
<output>2.5</output>

<gadget id="calculator">100 / 2.5</gadget>
<output>40</output>

<gadget id="calculator">1.5 * 40</gadget>
<output>60</output>

<result>60</result>