The master and the apprentice jointly assemble 50 machines, and each machine assembly must go through two processes, A and B. For each machine, the master needs 15 minutes to operate process A, and 5 minutes to operate process B; the apprentice needs 45 minutes to operate process A, and 20 minutes to operate the start-up process. Each process of each machine can only be completed by one person, and different processes can be completed. Completed by different people, but must A first B after. Ask: If two people cooperate, how many minutes will it take to complete the work?
师徒两人共同组装50台机器，每台机器组装必须经过A、B两道工序．对于每台机器，师傅操作A工序需要15分钟，操作B工序需要5分钟；徒弟操作A工序需要45分钟，操作启工序需要20分钟，每台机器每道工序只能由一人完成，不同工序可以由不同人分别完成，但必须A先B后．试问：如果两人合作至少要花多少分钟才能完成工作？
<result>755</result>