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Let the distance b x km 
time taken at 4 km/h = x/4 
time taken at 5 km/h = x/5 

but the difference in those two times is 9 minutes 
or 9/60 hrs = 3/20 hrs 

x/4- x/5 = 3/20 
times 20, the LCD 
4x - 4x = 3 
x = 3 
1 5 1