The level of dissolved oxygen in a water sample can be determined by the Winkler method. In a typical analysis, a 100.0-mL sample is made basic, and treated with a solution of MnSO4, resulting in the formation of MnO2. An excess of KI is added, and the solution is acidified, resulting in the formation of Mn2+and I2. The titrated I2is titrated with a solution of 0.00870M Na2S2O3 requiring 8.90 mL to reach the starch indicator end point. Calculate the concentration of dissolved oxygen as parts per million of O2.