求助一个操作系统很菜鸟的问题

suppose that a maltiprogrammed computer with a processor and two I/O device I/O 1 I/O 2 Jobs ，J1 J2 J3 have been loaded into main memory with the following resouresing sequenece
J1 I/O2 30m CPU 10m I/O1 30m CPU10m
J2 I/O1 20m CPU 20m I/O2 40m
J3 CPU 30m I/O1 20m
1) 优先级J2>J3>J1
2)高级优先级的作业可以抢占低级优先级的CPU 但不能抢占低优先级的I/O
1.Elapsed time of J1 J2 J3 ？
2.CPU utilization when all jobs are finished ?
3.I/O1 utilization when all jobs are finished ？