A fast-food restaurant operates both a drivethrough facility and a walk-in facility. On a randomly selected day, let X and Y, respectively, be the proportions of the time that the drive through and walk-in facilities are in use, and suppose that the joint density function of these random variables is: f(x, y) = 10, (x+2y), 0 x 1, 0 y 1, elsewhere. Find the covariance, Cov(X,Y).