Three electron emitters produce electron beams with changing kinetic energies that are uniformly distributed in the ranges [3,7], [2,5], and [4,10]. Let Y denote the total kinetic energy produced by these electron emitters. 

(a) Suppose that the three beam energies are independent. Determine the mean and variance of Y .

(b) Suppose that the covariance between any two beam energies is −0.5. Determine the mean and variance of Y .

(c) Compare and comment on the results in parts (a) and (b).