(based on knnl problem 15.13) an automotive engineer was interested in the effect of four al- ternative rubber compounds on the life of automobile tires. to carry out the study, five tires were manufactured from each of the four compounds and five automobiles were obtained for testing. with each automobile, the four tire types were assigned at random to the four wheels. each automobile was driven for 40,000 miles and the amount of wear on each of the four tires was recorded. a what is the experimental unit in this study? b what is the experimental factor, and what are the levels of this factor? c what non-experimental (observational) factor is present in this study, and what are the levels of this factor? d are the two factors crossed, nested or neither? explain your answer briefly. e what kind of design is this?