Suppose the regression model is estimated as follow: Y(hat) = 2475.8 - 114.378 X1i- 107.585 X 2i + 0.080 X3i + 2.420 X4i (s.e) (2145.5) (197.049) (127.492) (6.158) (2.219) R2 = 0.98 N = 100 DW statistics = 1.591 a) Test the existence of serial autocorrelation for the above model. b) State three (3) ways of correcting the problem in(a)