∑A football goalkeeper moves across her goal in a straight line. Her motion is shown on the following graph of horizontal position xxx vs. time ttt. Graph of x (in meters) vs. t (in seconds). The y-intercept is at (0,0), then x increases linearly from 0 m to 2 m over 4 s, stays constant at 2 m from 4 to 8 seconds, and then decreases linearly from 2m to 0 m between 8 s and 12 s. Graph of x (in meters) vs. t (in seconds). The y-intercept is at (0,0), then x increases linearly from 0 m to 2 m over 4 s, stays constant at 2 m from 4 to 8 seconds, and then decreases linearly from 2m to 0 m between 8 s and 12 s. What is the average speed of the goalkeeper between the times t=4\text{ s}t=4 st, equals, 4, start text, space, s, end text and t=12\text{ s}t=12 st, equals, 12, start text, space, s, end text?