He ran for 12 km in his journey.
<h3>What is an Equation ?</h3>
An equation is formed when two algebraic expressions are equated by an equal sign.
It is given that
Speed of Walking =6km/hr
Speed of Running = 15km/hr
Let he walks and run x hours ( as given)
he covered distance = 21 x km
The total time taken in the journey is 2x
for the same distance
It is also given that
if for the total journey
if he walks walked twice as long on the journey
He walked 6x in the journey so new distance that he walked is 12x , then the total journey time = 6 minutes longer
Converting speed from km / hr to km/ min
1 km / hr = 60 km/ min
and forming an equation with the given data
12x * 60 /6 + 9x *60/15 = 2x * 60 + 6
120x + 36x = 120x +6
150x = 120
x = 120/150
x = 0.8 hours.
Therefore he spent 0.8 hours walking and 0.8 hours running and He ran 15 * 0.8 = 12 km
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