Question 941508
speed of Joe  = 70 miles per hr
speed of Bob = 55 miles per hour
since both are travelling in the same direction , relative speed  = 70-55
                        = 15 miles per hour
already Bob, 80 miles ahead before start of joe
Joe has to cover 80 miles with relative speed 
   time  =  distance  / speed
          = 80 /15
          =5.33 hours
               =  5 hrs+0.33 hr  (1 hr  =60 min)
   = 5 hr  +0.33*60
    =5 hr +20  min
 Result : 5 hours 20 minutes