Why is it that the number of hours in the day never change yet some days fly by and others drag on? ?

because the season change if you are in summer the days seem longer because the sun stays up longer if you are in the winter the days seem shorter because the sun goes down sooner.

If you're referring to why time flys by so fast or slow depends on what you're doing to keep yourself occupied. I guess that's what you are asking?

the total distance traveled by the car is

30km + 49km = 79 km .

it is a negative acceleration