In the COD measurement of a raw wastewater sample, initial K2Cr2O7 concentration added into the wastewater sample is 3.000 g/L.

In the COD measurement of a raw wastewater sample, initial K2Cr2O7 concentration added into the wastewater sample is 3.000 g/L. After the redox reaction has reached an equilibrium, the K2Cr2O7 concentration has been reduced to 1.824 g/L. Assuming in the redox reaction, the Cr in K2Cr2O7 is reduced to Cr3+. What is the COD of the wastewater sample in mg/L? Please show all work. Thank you!