(35 points) assume that pa, pb and pc are three distinctive programs. assume that when pa is executed, it forks new processes executing pb at tick-marks 2 and 5, it does an i/o request at tick-mark 4, and its burst time is 8. assume that when pb is executed, it forks new processes executing pc at tick-marks 2 and does an i/o request at tick-mark 3, and its burst time is 6. assume that pc has a burst time of 4 and it does an i/o request at tick-mark 2. assume that two processes p1 and p2 have arrived before t=0; and p1 is executing pa while p2 is executing pb. assume that each i/o request can be completed within 3 ticks and i/o requests are handled in a fcfs manner. draw a gantt chart illustrating the scheduling if a fcfs scheduling is used. mark on the chart when a process is arrived and finished.