Hello! Gramatically, let's look at each choice-
(a) says: Mrs. Anderson flies to Sweden tomorrow her plane leaves at 2:00 P.M.
This can't be right, because it's a run-on sentence! If someone were to say this outloud, it would sound as if someone wasn't "taking their time"!
(b) says: Mrs. Anderson flies to Sweden tomorrow, her plane leaves at 2:00 P.M.
This one looks correct. It has a comma which adds a pause. It also connects both statements made in the sentence.
(c) says: Mrs. Anderson flies to sweden tomorrow, and her plane leaves at 2:00 P.M.
This one wouldn't be correct because its listing ideas with "and" in between. It's as if the speaker is saying "she does this and this and that and that..."
So your best choice would be B.
