Average speed for a 42.2 km marathon run in 3 h 53 min 17 s

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The question states that Running a marathon backwards the record is 3 h 53 min 17 s and the race is 42.2 km's and I am supposed to calculate avreage speed of the race in meters per second and kilometres per hour I found a way to convert the record into just hours and I divided by 42.2 and the answer was completely wrong because according to the book its 10.9km/h and 3.01m/s does anyone have any idea how to achieve this answer?
 
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[tex]s=\frac{d}{t}[/tex]
Speed is km/h, not h/km.
 
_wantana said:
The question states that Running a marathon backwards the record is 3 h 53 min 17 s and the race is 42.2 km's and I am supposed to calculate avreage speed of the race in meters per second and kilometres per hour I found a way to convert the record into just hours and I divided by 42.2 and the answer was completely wrong because according to the book its 10.9km/h and 3.01m/s does anyone have any idea how to achieve this answer?
Show your conversion of time to hour.