4. (25 points) In an experiment conducted in an engineering department, growth of a certain type of algae in water was observed as a function of time and the dosage of copper added to the water. The data are as follows. Response is in units of algae. Time in Days Copper 5 12 18 1 0.30 0.37 0.25 0.34 0.36 0.23 0.32 0.35 0.24 2 0.24 0.30 0.27 0.23 0.32 0.25 0.22 0.31 0.25 3 0.20 0.30 0.27 0.28 0.31 0.29 0.24 0.30 0.25 Source of Sum of Degrees of Mean Variation Squares Freedom Square Time 0.025622 0.012811 N N Copper 0.008956 0.004478 Time*Copper 0.012756 4 0.003189 Error 0.005933 18 0.000330 (a) (5 points) Comment on the analysis-of-variance results shown above. Does the level of copper impact algae concentration? (b) (10 points) Comment on the results of the test for interaction. How is the effect of copper content influenced by time? Plot the interactions in one figure and write concluding statement. (c) (10 points) Do contrast analysis by comparing copper 1 versus 2 and 3. Plot and write concluding statement