In Process1 first 2 unit for IO, next 7 unit for computation, next 1 unit for IO
In Process2 first 4 unit for IO, next 14 unit for computation, next 2 unit for IO
In Process3 first 6 unit for IO, next 21 unit for computation, next 3 unit for IO
In Process4 first 8 unit for IO, next 28 unit for computation, next 4 unit for IO
IO time will overlap with if some other process want to compute then
Gantt chart
0______2(I/O time)|_____________P1_______________9(Process1)
__________P2______________23(Process2)________P3_________44(Process3)___________________
P4_____________72(Process4)_________4(I/O)_________76
So, among 76 unit time
6unit used for IO
72 unit require for process to complete
So, in IO time in percent $\frac{6}{76}\times 100=7.8$