Answer: a) 720, b) 24, c) 0.0333....
Explanation:
Since we have given that
Number of people = 6
In how many ways can they arrive?
So, total possible ways would be

In how many ways can Jean arrive first and Keith last?
Since Jean take first place and keith takes the last place.
Remaining people = 4
so, number of ways would be

Find the probability that Jean will arrive first and Keith will arrive last.
So, probability would be

Hence, a) 720, b) 24, c) 0.0333....