How do I solve

2.2 A wastewater sample with a DO content of 1.4 mg/L is diluted with deionized water with a DO content of 8.8 mg/L in a 300 mL BOD bottle. The DO content of the diluted sample during a BOD test at 25 C is 7.8 mg/L initially, 3.2 mg/L after 7 days, and 1.5 mg/L after an indefinitely long period of time. (a) Determine the volume of the undiluted wastewater sample used. (1 mark) (b) Determine the BODs of the undiluted wastewater sample if a test is conducted at 20 C. (7 marks)