The way you have it doesn't make sense.  All the planes I've seen fly a little
faster than 4.8 miles per hour, because you can walk that fast.

Here's a way it could have been:

Johnny flew 2100 miles Miami to SF against the wind while his girl friend flew
from SF to Miama with the wind in 4.8 hours.  They communicated by cell phone
and kept their air speed indicators exactly the same speed the whole way. It
took him 5.6 hours and her 4.8 hours. 

x = air speed (how fast they would be going if the air was still.

         distance    rate      time
Johnny     2100      x-w       5.6 
girl       2100      x+w       4.8

           2100 = (x-w)5.6
           2100 = (x+w)4.8

Multiply the first by 5.6 and the second by 4.8

            375   = x - w
            437.5 = x + w

Add the equations get 

           812.5 = 2x
          406.25 = x

Multiply the first by -1 and add

            -375  = -x + w
            437.5 =  x + w
             52.5 =     2w
            25.25 = w

So the airspeed they kept their planes at was 406.25 mph and
the wind was blowing 25.25 miles per hour toward the west.

That's probably not the way it was stated but at least that
makes a little more sense.

Edwin