> summary(m3.1) 

Coefficients:
             Estimate Std. Error t value Pr(>|t|)    
(Intercept) 12.915676   0.502463  25.705  < 2e-16 ***
V5           0.287077   0.108717   2.641  0.00873 ** 
V8          -0.033139   0.020466  -1.619  0.10649    
V11          0.402557   0.042078   9.567  < 2e-16 ***
---

Residual standard error: 0.3505 on 289 degrees of freedom

> extractAIC(m3.1)
[1]   10.0000 -617.0269