Use the Body Fat data set to answer the following:

(a) Regress Density on Age, Height, Neck, Chest, Abdomen, Hip, Thigh, Knee, Ankle, Biceps, Forearm, Wrist.

(b) Check the assumptions associated with this model. Be sure to plot the standardized residuals versus each of the explanatory variables, check for collinearity, and check the normality assumption.

(c) Identify any influential observations.