A worker processes a batch of parts, the original plan is to process 20 parts per hour, and it can be completed in 12 hours. The actual processing is 4 more per hour than the original plan, how many hours can actually be completed?
一个工人加工一批零件，原计划每小时加工20个，12小时可以完成．实际每小时比原计划多加工4个，实际多少小时可以完成？
<result>20</result>