Which equation is most likely used to determine the acceleration from a velocity vs. time graph?

Essentially the slope will be the acceleration in a velocity-time graph. This is because when you are finding the slope for the velocity-time graph, it would be velocity (the y value), divided by time (the x value). (The formula for finding the slope is: y2-y1/x2-x1). And, as you may know, the formula for acceleration is velocity divided by time. In conclusion the finding the slope will give you the acceleration in a velocity-time graph.