3 1/2 miles in 1 1/4 hours

Simple, take 3 1/2 turn it into a decimal which = 3.50 since

1/2 = 0.5 because 1 divide by 2 = 0.5

Same thing for 1 1/4 = 1.25 since

1/4 = 0.25 because 1 divide by 4 = 0.25

3.50 divide by 1.25 = 2.8 miles one hour.