Question 35835
Draw the picture.
Label the start point "O"
Label the crossroad "C"
OCB is a right angle.
Tom Data:
Tom walks 0C then CB
CB is 4 miles and takes 6 hrs.
Therefore Tom's walking rate is 4/6 = (2/3) mi/hr
Tom walks OC in 4 hours.
Therefore OC is (2/3)(4)=(8/3) mi.
John Data:
John walks path OB
OB is the hypotenuse of a rt. triangle with side 
OC=(8/3)mi. and side CB=4 mi.
Using Pythagoras you can find that OB = 4.8 miles
Therefore John's walking rate is 4.8/10 = 0.48= 12/25 mi/hr.

Cheers,
Stan H.