For the estimated equation y_hat = beta_0 beta_1_hat X_1 beta_2_hat X_2 beta_3_hat X^2_1 beta_4_hat X^2_2 beta_5_hat (X_1 * X_2). what is the predicted effect from a one-unit increase in x_2, holding x_1 constant? a). beta_2_hat 2beta_4_ hat X_2 beta_5_ hat X_2 b). beta_2_hat 2beta_4_ hat X_2 beta_5_ hat X_1 c). beta_2_hat 2beta_4_hat X_2 d). beta_2_hat 2beta_4_hat X_1