the time it takes is distance / speed for each way.
so, the total time is:
dry time + wet time = distance/dry speed + distance/wet speed
and we also know that dry speed = wet speed * 2
so we can replace the terms we know in the previous equation.
total time = 60/(2* wet speed) + 60/wet speed = 30/wet speed + 60/wet speed = 35
90/wet speed = 35
wet speed = 90/35 = 45/7 = 6.4 mi/hr so dry speed is twice that at 12.8
