The answer is as follows: the number of sides of this regular polygon is n.

(n-2)× 180= 120n

60n=360

n=6

The number of sides of this regular polygon is 6.

The second question:

Solution: When you set up a car, the uphill journey is X kilometers, the downhill journey is Y kilometers, and the flat road journey is Z kilometers.

X+Y+Z= 142( 1)

X/28+Y/35+Z/30=4.5(2)

X/35+Y/28+Z/30=4.7(3)

The solution is X=42.

Y=70

Z=30