Each front tire on a hybrid is assumed to be filled to the pressure of 26 psi. Assume the actual air pressure in each tire is the random variable: X for the right tire and Y for left tire with the joint pdf. f(x,y) = k(x2 + y2) for 20 ? x ? 30 and 20 ? y ? 30 where k = 3/380,000. Find the correlation coefficient ? for X and Y.