The marketing department for an upscale retail catalog company wants to determine if there are differences in the mean customer purchase amounts across the available purchase sources (Internet, phone, or mail-in). Accordingly, samples were taken for 20 random orders for each purchase source. The ANOVA table produced shows that 553 (sum of squares between groups) = 12715.23 and SST (sum of squares total) = 849419.93. Based on this information, the degrees of freedom corresponding to MSB (mean square between) in the numerator is equal to