The graph of velocity vs t permits estimate the acceleration because acceleration is the change of velocity respect time.
The change of velocity is the derivative of the velocity function, which is the same that the slope of the tangent line in the desired point.
The graph provided by you contains the tangent lines, so you can easily find the slope for the poiints x and y.
Point x:
The tangent line is horizontal, then the slope is zero, which means that at this point the acceleration is zero.
Point y: the the slope of the tangent line is rise / run = Δv / Δt =
= (5 - 0 m/s) / (7 - 12 s) = 5 / (-5) = - 1 m/s^2 = acceleration at point y
Answers: 0 and - 1 m/s^2
