Acar traveled twice as fast on a dry road as it did making the return on a slippery road. the trip was 60 mi each way, and the round trip took 35 hr. what was the speed of the car on the dry road?

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