Answer:
89.01% probability that a flight arrives on time given that it departed on time.
Step-by-step explanation:
We use the conditional probability formula to solve this question. It is

In which
P(B|A) is the probability of event B happening, given that A happened.
is the probability of both A and B happening.
P(A) is the probability of A happening.
In this question:
Event A: Departing on time
Event B: Arriving on time.
The probability that a flight departs and arrives on time is 0.81.
This means that 
The probability that an airplane flight departs on time is 0.91.
This means that 
Find the probability that a flight arrives on time given that it departed on time.

89.01% probability that a flight arrives on time given that it departed on time.