Option D at 8pm
6 technicians take 10hrs to build a server or to complete = a work
1 technician cn work in 1 hr is= 1/10*6 work
Work done by 6 technicians in 6hr (11 am to 5pm)= 6*6/10*6 work
= 6/10 Work
Remaining work 1-6/10= 4/10 work
For next 1 hr one technician is added ( 6pm)
So work done by 7 technician 1 hr = 7*1/10*6 work = 7/60 work
Remaining Work= 4/10 -7/60= 17/60work
For next 1 hr one technician is added ( 7pm)
So work done by 8 technician 1 hr = 8*1/10*6 work = 8/60 work
Remaining Work= 17/60 -8/60= 9/60work
For next 1 hr one technician is added ( 8pm)
So work done by 9 technician 1 hr = 9/10*6 work = 9/60 work
= Remaining Work 9/60 - 9/60=0 Remaining work
Server will br completed at 8 pm