Answer:


Since X and Y are independent then
and we have this:

And the deviation would be given by:

And then the distribution for the total time would be given by:

Explanation:
For this case we can assume that X represent the flight time for the first filght and we know that:

And let Y the random variable that represent the time for the second filght and we know this:

And we can define the random variable Z= X+Y as the total time for the two flights.
We can asume that X and Y are independent so then we have this:


Since X and Y are independent then
and we have this:

And the deviation would be given by:

And then the distribution for the total time would be given by:
