The master and apprentice process parts, the apprentice makes 40 parts per hour, and the master makes 60 parts per minute. The apprentice processed for 15 minutes before the master started processing. After a few minutes, the master will process as many pieces as the apprentice?
师徒俩人加工零件，徒弟每小时做40个，师傅每分钟做60个．徒弟先加工了15分钟后，师傅才开始加工．师傅几分钟后加工的个数和徒弟一样多？
<result>30</result>