In a laboratory experiment, data were gathered on the life span (Y in months) of 33 rats, units of daily protein intake (X1), and whether or not agent X2 (a proposed life extending agent) was added to the rats diet (X2 = 0 if agent X2 was not added, and X2 = 1 if agent was added.) From the results of the experiment, the following regression model was developed.
Yˆ=36+0.8X1-1.7X2
Also provided are SSR = 60 and SST = 180.
The test statistic for testing the significance of the model is?