Consider a regression model to estimate the treatment effect: Yit= B0 B1Xit B2Gi B3Dt Uit where G is the group dummy that takes value 1 for individuals in the treated group, and D is the post-treatment period dummy which takes value 1 for the period in which the treated group has received the treatment. X is defined to be G x D. Suppose that the estimated parameters are (^B0,^B1,^B2,^B3) = (1.20, -1.33, 0.52, -3.0) What is the estimated treatment effect