The file P12_29.XLS gives the miles per gallon for each of three different octanes (Octane A, Octane B, and Octane C) of gasoline and three types of vehicles (light, medium, and heavy). Subsets of ten vehicles of each type have been randomly assigned to each octane level. 

a. Do you find evidence of a significant main effect for the octane factor in this case? Explain. 

b. Do you find evidence of a significant main effect for the vehicle type factor in this case? Explain. 

c. Do you find evidence of significant interactions between the two factors in this case? Explain.