Sam is observing the velocity of a car at different times. after two hours, the velocity of the car is 54 km/h. after four hours, the velocity of the car is 58 km/h.

part a: write an equation in two variables in the standard form that can be used to describe the velocity of the car at different times. show your work and define the variables used. (5 points)

With that information you can only suppose a uniformly accelerated motion.  This is, acceleration is constant.

Then, acceleration = change in velocity / change in time = (58 -54)km/h / 2 h = 4km/h / 2 h = 2 km/h^2

Then the equation for velocity, V is

V = Vo + a*t = Vo + 2 (km/h^2)  * t = Vo +  2t

Vo is the initial velocity, which you can find using V = 54km/h and t = -2

Vo = V after 2 hours - a*(2hours) = 54km/h - 2(km/h^2)*2h = 54km/k - 4km/h = 50km/h

Then, the equation is: V = 50 km/h + 2t

Valid for constant acceleration. 

Does this your question?