A car is traveling on a long straight road. it starts at the origin t=0 and mices with velocity of t 9.0 m/s for 30 s. after stopping for 10s at a crosswalk to allow a pedestrian to cross the road, it them moves at t 6.0 m/s for another 20 s. (a) what is the final position of the car? (b) what is the car’s average velocity

I suggest you post this as a physics question. This is NOT chemistry.

9 m/s * 30s = 270m

6 m/s * 20s = 120m
(a) 390 m
(b) 390m/(30+10+20)s = 390/60 = 6.5 m/s