um I think you need to multiply 10 km by 2.1
10 Km. S= Speed D= distance T= time
S= d/t but since you are solving for "d" the equation is d=st so you plug in 10 km/h for speed and 2.1 hours for time and just multiply them. The hours cancel out so you are left with 10km.
The runner will travel a total distance of 21 kilometers if she runs at an average speed of 10 km/hour for 2.1 hours.
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