John bikes for 2 hours at a speed of 15 miles per hour. how many hours will it take shannon to cover the same distance at a speed of 10 mi/h?

if john bikes for two hours 15 miles per hour two hours is thirty miles of biking
D=RT
Distance= 30 miles 
Rate= 10 miles per hour 
Time= t 
plug numbers in 
30 = 10t 
divide each side by ten to get t by itself 
t= 3 
time = 3 
3 hours to travel 30 miles biking at 10mph