Let D be the distance under the question, in kilometers. Then your "time" equation is- = 0.5 of an hour. To solve the equation, multiply both sides by 300: 6D - 5D = 300*8.5 D = 150. Answer. The distance under the question is 150 kilometers. Check. The time to cover 150 km at 50 km/h is = 3 hours. The time to cover 150 km at 60 km/h is = 2.5 hours. The difference of times is 3 - 2.5 = 0.5 hours. ! Correct !