Min time required [without simultaneous occurrence ]
Only one instruction at a time i.e. I3 .
Response time + Execution time=4.5+20=24.5
Max time required
All instructions are present.
i.e.=I1+I2+I3 ={(4.5+25) +(4.5+35) +(4.5+20) }
=93.5
So possible range of I3 24.5 microsecond to 93.5 microsecond .