Question 284678
Let the total distance covered be x miles.
Let him take 't' minutes to go to gym by walking
& (45-t) min for returning by driving. OK.
 
Distance = speed * time. OK.

x = 6 mph * t

also 

x = 48 mph * (45-t)

Thus:

=>  6 mph * t = 48 mph * (45-t)

On solving t = 40 min(for walking ,so 5 min for driving) .OK.

Thus x = 6 * 40 = 240 miles......

Happy....