The discharge of industrial wastewater into rivers affects water quality. To assess the effect of a particular power plant on water quality, 24 water specimens were taken 16 km upstream and 4 km downstream of the plant. Alkalinity (mg/L) was determined for each specimen, resulting in the summary quantities in the accompanying table. Do the data suggest that the true mean alkalinity is higher downstream than upstream by more than 50 mg/L? Use a .05 significance level.

Location n Mean Standard Deviation Upstream 2 75.9 1.83 Downstream 24 183.6 1.70