A and B produce a total of 180 parts in 4 hours. It is known that A makes 25 parts per hour, how many parts does B make per hour?
甲和乙4小时共生产零件180个，已知甲每小时做25个，乙每小时做多少个？
<gadget id="calculator">180 / 4</gadget>
<output>45</output>

<gadget id="calculator">45 - 25</gadget>
<output>20</output>

<result>20</result>