please answer these questions! Thank you:)

A researcher studied the effects of three experimental diets with varying fat contents on the total lipid (fat) level in plasma. Total lipid level is a widely used predictor of coronary heart disease. Fifteen male subjects who were within 20 percent of their ideal body weight were grouped into five groups according to age. within each group, the three experimental diets were randomly assigned to the three subjects. Data on reduction in lipid level (in grams per liter) after the subjects were on the diet for a fixed period of time follow. (a) Identify the experimental design used here. Be very specific, and make sure that you identify the treatment and design structures, and which factors are treatment factors and which are blocking factors. (b) Conduct the ANOVA table and test a proper hypothesis. (c) obtain the residuals for the model in (a) and plot them against the fitted values. Also prepare a normal probability plot of the residuals. What are your findings? (d) Now we assume the randomized complete block design. Conduct the Tukey test for additivity of block and treatment effects