if the number in the numertor at a constant speed after 20 min the boat has traveled 2.5 miles the bost traveles a total of 10 miles to a br

A boat travelling at a constant spedd traveling 2.5 miles in 20 minutes:

     Distance   =   rate x time

       2.5 mi    =   rate x 20 min     --->     rate  =  2.5mi / 20 min     =  0.125 miles per minute

If the boat travels a total of 10 miles:

     Distance   =   rate x time

     10 miles   =   0.125 mi/min x time     --->     time  =  10 mi ÷ 0.125 mi/min     =     80 minutes