A box proceeds along the x-axis and the figure below shows a record of its velocity as a function of time. Every gridline along the vertical axis corresponds to 3.00 m/s and each gridline along the horizontal axis corresponds to 4.00 s. (Enter your answers in m/s2. Indicate the direction with the signs of your answers. Note that t = 0 at the intersection of the axes.) (a) Determine the average acceleration of the box in the time interval t = 0 to t = 20.0 s (b) Determine the average acceleration of the box in the time interval t = 20.0 s to t = 60.0 s (c) Determine the average acceleration of the box in the time interval t = 0 to t = 80.0 s