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

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.

the change is the difference between final velocity and initial velocity

5-1 = 4m change in velocity