Class A has 120 books, and Class B has 30 books. How many books does Class A give to Class B? The number of books in Class A is twice that of Class B.
甲班有图书120本，乙班有图书30本，甲班给乙班多少本，甲班的图书是乙班图书的2倍．
<gadget id="calculator">120 + 30</gadget>
<output>150</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">150 / 3</gadget>
<output>50</output>

<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<result>20</result>