B1	B2
A1	n = 10 T = 40 SS = 70	n = 10 T = 10 SS = 80
A2	n = 10 T = 30 SS = 73	n = 10 T = 20 SS = 65

N = 40, G = 100, G²/N = 250, ² = 588

For these data, what is df_{within treatments}?