A computer can perform 30 identical tasks in six hours. At that rate, what is the minimum number of computers that should be assigned to complete 80 tasks within three hours?

We Know
Total work = rate × Time

therefore
30 = Rate × 6
or Rate = 30/6 = 5

Now we need to find the number of computers
total work given = 80 and total time = 3 hrs

therefore
80 = 5 × 3 × No. of computers
or No. of computers = 80/15 = 5.333 , but no. of computers cannot be fraction i.e , so we have to consider as 1.

Total no. of computers = 5 + 1 = 6.