The speed of a runner increased steadily during the first three seconds of a race. Her speed at half-second intervals is given in the table. Find lower and upper estimates for the distance that she traveled during these three seconds.
t (s) 0 0.5 1.0 1.5 2.0 2.5 3.0
v (ft/s) 0 6.2 10.8 14.9 18.1 19.4 20.2