The population mean brain-weight at 90 days of age for a particular strain of inbred mice is 3.36 grams. A group of 25 of these mice are reared in a special environment designed to stimulate diverse kinds of learning. The 90-day mean brain-weight of these mice is 3.40 with sx = .05. Test the hypothesis that the special environment has no effect on brain-weight. Use = .05.