Math word problem help!?

Question

here is the problem. i know the answers, i just dont know how to get them.

Two planes start at the same place and travel in opposite directions, one at 520 mph and the other at 448 mph. How many hours will it take for them to be 1936 miles apart?

Answer 1

the answer is 2 hours. 520x2+ 448x2 = 1936

or 520+448x 2=1936

they will travel a total of 968 miles apart per hour