A data set in the R software is called trees. There are observations of a=girth (in inches) and ry=height (in feet), and y=volume (in cubic feet) on 31 black cherry trees. The sample mean girth was 13.2 and the sample mean height was 76.0. Centred variables cgirth=girth-13 and cheight-height-76 were created and the following two regression equations were fit, and cross- validated root mean squared errors were computed. fit1=lm(Volume"cgirth+cheight) # Model 1 Estimate Std. Error t value Pr(>It[) (Intercept) 29.0015 0. 7003 41. 414 |t[ ) (Intercept) 26.57619 0. 62927 42.233