Use the following information to answer question 26-29.
Shasta is participating in a bike ride for charity. The graph of speed (s) versus time (t) for the first 20 seconds of her bike ride is shown in the coordinate plane below. The graph is composed of 2 line segments for which the endpoints are at (0,0), (10,5), and (20,3). Shasta traveled 25 meters in the first 10 seconds.
Beginning at t = 20 seconds, Shasta slows down as she approaches a familiar group of riders ahead of her and then travels at a constant speed with the group after joining them.
27. Shasta's acceleration, a, over the interval from t = 10 seconds to t = 20 seconds, is equal to the slope of the graph over that interval, measured in meters per second per second. What is the value of a?