Distribute a batch of books to three classes A, B, and C according to 3:2:1. It is known that class B gets 30 books. How many books are there in this batch?
将一批书按3：2：1分配给甲、乙、丙三个班，已知乙班分得30本，这批书共多少本．
<gadget id="calculator">3 + 2 + 1</gadget>
<output>6</output>

<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">30 / (1/3)</gadget>
<output>90</output>

<result>90</result>