4.Four processes execute on a system with a single CPU and a single I/O device. The system uses multiprogramming without time-sharing. Each process has a compute-bound phase of 30 time units followed by an I/O-bound phase of 60 units. A process cannot initiate the I/O phase until the I/O device becomes free. The processes start executing in the order p1, p2, p3, p4. During the execution of all processes,

a. how many time units is the CPU in the idle state?

b. how many time units is the I/O in the idle state?