part b is more important tor me i got a already pkease do it with dteps i need to ubderstand

2. In a BOD test, 100 mL of a wastewater sample and 200 mL of dilution water were added to a 300 ml bottle. The initial dissolved oxygen concentration in the bottle was 9.0 mg/L. After 5 days, the dissolved oxygen concentration in the bottle was 5.5 mg/L, and after 10 days, the oxygen concentration was 4.5 mg/L. After 20 days, the oxygen concentration stabilized at 4.0 mg/L. a. Calculate the BODs of the sample. 5/10 b. Calculate the ultimate BOD of the sample