Let radius = ru00a0speed = vno of pipes = 4total time = 9 hoursSo, total volume = (pie * r^2) * 9 * v * 4Now, new radius = r/2new speed= 3vtotal time = 6 hours n of pipes be xSo, (pie * r^2) * 9 * 4 = (pie * (r/2)^2) * 6 * 3v * xi.e x = 88 Pipes are required.