Assertion (A): Activity 57 is critical. Reason (R): Earliest finish time and latest finish time for events 57 are same A. A is correct but R is not correct B. R is correct but A is not correct C. Both A and R is correct D. Both A and R is incorrect

The correct answer is C. Both A and R are correct.

An activity is critical if any delay in its start or finish will delay the project completion. The earliest finish time (EFT) of an activity is the earliest time at which the activity can be completed, given the start times of its predecessors. The latest finish time (LFT) of an activity is the latest time at which the activity can be completed without delaying the project completion. An activity is critical if its EFT and LFT are the same.

In this case, activity 57 has an EFT and LFT of 10, so it is critical. The reason is also correct, as the EFT and LFT of activity 57 are the same.