Question

Assume that the average speed of a moving object at 1 m was initial velocity and average spped of your cvart 5 m was its final velocity. calculate the change in velocity of your cart from 1 m to 5m. Show your work

Answer 1

Sinc you don't give numbers for initial and final velocity, the change in velcity was just
(final velocity) - (initial velocity)

It makes no sense to talk about the average velocity at an instant, as your question has done.

Answer 2

the change is the difference between final velocity and initial velocity

5-1 = 4m change in velocity