29. The graph at the right shows the rate, r(t), in hundreds of algae per hour, at which a population of algae is growing, where t is in hours. 25 20 15 10 a) Estimate the average value of the rate over the first 2.5 hours. b) Estimate the total change in the population over the first 3 hours. r(t) 5 0 5 -10 -15