Average speed, and total distance traveled

[Porcelain]

Homework Statement

Sally travels by care from on city to another. She drives for 30.0 min at 80.0 km/h, 12.0 min at 105 km/h, and 45.0 min at 40. km/h, and she spends 15.0 min eating lunch and buying gas.
a.) Determine the average speed for the trip.
b.) Determine the total disance traveled.

Homework Equations

Vavg= total distance/time
Vavg=change in displacement/time

The Attempt at a Solution

a.) is 53.5, and b.) is 91 but I am not sure how to get them.
My friend was trying to explain it to me, and said to turn all the minutes into hours and multiple them by the speeds. I did that and got 91, but I am not sure why i had to do that.

 

[Quincy]

what are the units of 53.5? Give units in your answers.

 

[Porcelain]

a.) is km/h and b.) is km, i figured it out though.