The defendant served the plaintiff, by mail, a motion for summary judgment on April 14, 1983. According to D.C.C.R. 6(e), when service of a motion is made by mail, 3 days must be added to the prescribed period for responding to the motion. Three days added to April 14 is April 17. April 17,1983, was a Sunday; therefore, one day must be added making April 18, 1983, the date from which computation of the prescribed period must begin. D.C.C.R. 6(a). The plaintiff had 15 days within which to respond to the defendant’s motion for summary judgment. D.C.C.R. 78(b)(1). Thus, the plaintiff had until May 3, 1983, to file a memorandum in opposition to the defendant’s motion. The trial court issued its order granting the motion for summary judgment on May 2, 1983, one day before the plaintiff’s time for filing an opposing memorandum had elapsed. Since D.C.C.R. 78(b)(1) was not complied with, the trial court’s order granting the defendant’s motion for summary judgment is reversed.