求教各位老大!!!

救命啊,下星期要考試,晚上要打工, 作業都沒法做了.請教各路高人,以下這題怎麽做啊??

If program A has a total of run time of 40ms and IO time of 100ms,
If program B has a total of run time of 60ms and IO time of 20ms,
If program C has a total of run time of 30ms and IO time of 700ms,

there is only one IO device, and one CPU, what is the minimum total time to run these three programs?(show your steps)
The question is about Concurrency.

跪謝各位了!!!