The following data have been obtained in a BOD test that is made to determine how well a wastewater treatment plant is operating

| | Initial DO (mg/L) | Final DO (mg/L) | Volume of Wastewater (mL) | Volume of Dilution Water (mL) |
| Untreated Sewage | 6.0 | 2.0 | 5 | 295 | Demand |
| Treated Sewage | 9.0 | 4.0 | 15 | 285 | Demand |

What percentage of the BOD is being removed by the treatment plant?
BODS = (DOi - DOf) / P
P = dilution factor (volume of wastewater / volume of wastewater plus dilution water)
a. 85%
b. 68%
c. 58%
d. 45%