Worker A binds 420 books in 6 hours, and the number of books bound per hour is 12 more than that of worker B. How many books does worker B bind per hour?
甲工人6小时装订书籍420本，每小时装订的本数比乙工人多12本，乙工人每小时装订多少本书籍？
<gadget id="calculator">240 / 6</gadget>
<output>40</output>

<gadget id="calculator">40 - 12</gadget>
<output>28</output>

<result>28</result>