There are two bookshelves A and B. It is known that A bookshelf has 540 books, which is 30 times less than that of B bookshelf. How many books are there on shelf B? (Solution problems of column equations)
有甲、乙两个书架．已知甲书架有540本书，比乙书架的3倍少30本．乙书架有多少本书？(列方程解应用题)
<gadget id="calculator">540 + 30</gadget>
<output>570</output>

<gadget id="calculator">570 / 3</gadget>
<output>190</output>

<result>190</result>