t=s/2v=3/2v=9/6v
If there are uphill and downhill,
The total time is the time required to go uphill plus the time required to go downhill.
t = 1/v+2/3v = 2/v = 5/3v = 10/6v
Compare it twice.
The denominator is the same, the bigger the numerator, the bigger the number, so the less time it takes to level the road.
In less time.
10/6v-9/6v= 1/6v