Answer:
9 km
Explanation:
Let's say he takes x hours going from point A to point B and y hours going back
y = x - 15 minutes
note that x is in hours, so we must convert
15 minutes = 1/4 of an hour = 0.25 hours
y = x - 0.25 hours
distance = speed * time
on the way there:
distance = 12 km/hr * x
on the way back:
distance = 18 km/hr * y
plug y = x-0.25 hours into the way back equation
distance = 18 km/hr * (x-0.25 hours)
distance = 12 km/hr * x
the distance is the same, so set these equations equal to each other
12 km/hr * x = 18 km/hr * (x-0.25 hours)
12 km/hr * x = 18 km/hr * x - 4.5 (km/hr * hours) = 18 km/hr * x - 4.5 km
subtract 18 from both sides to put all variables on one side
-6 km/hr * x = -4.5km
divide both sides by -6 km/hr to isolate x
x = 4.5/6 hours = 3/4 hours = 45 minutes
distance = 12 km/hr * 3/4 hours = 9 km