A has 130 books and B has 70 books. After B gives A some books, the number of A and B is 4:1.
甲有130本书，乙有70本书，乙给甲多少本书后，甲与乙的本数是4：1．
<gadget id="calculator">4 * 70</gadget>
<output>280</output>

<gadget id="calculator">280 - 130</gadget>
<output>150</output>

<gadget id="calculator">1 + 4</gadget>
<output>5</output>

<gadget id="calculator">150 / 5</gadget>
<output>30</output>

<result>30</result>