In sentencing defendants on drug conspiracy conviction, Dist. Ct. did not err in determining that participants in drug conspiracy produced and distributed 700 grams of heroin per week. Dist. Ct. could find officer believable in his testimony that one member of conspiracy calculated heroin sales at 700 grams per week, and Dist. Ct. was not required to believe other members of conspiracy who calculated heroin sales at 250 grams per week. Moreover, Dist. Ct. could properly apply 700 figure to all members of conspiracy. Dist. Ct. erred, though, in applying as to one defendant two-level enhancement under section 2D1.1(b)(1) of USSG for possession of firearms by other members of conspiracy, where record did not indicate that said defendant was aware of presence of firearms during operations of conspiracy.