The effects of developer strength (factor A) and development time (factor B) on the density of photographic plate film were being studied. Two strengths and two development times were used, and four replicates in each of the four cells were evaluated. The results (with larger being best) are stored in Photo and shown in the following table:

At the 0.05 level of significance,
a. is there an interaction between developer strength and development time?
b. is there an effect due to developer strength?
c. is there an effect due to development time?
d. Plot the mean density for each developer strength for each development time.
e. What can you conclude about the effect of developer strength and development time on density?