The school bought audio tapes for 5 yuan per box, and bought 20 boxes in total. If you use this money to buy 4 yuan a box of blank tapes, how many more boxes can you buy?
学校买录音磁带，每盒5元，一共买了20盒．如果用这些钱买4元一盒的空白磁带，可以多买多少盒？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<gadget id="calculator">25 - 20</gadget>
<output>5</output>

<result>5</result>