please explain step by step

7. The following results have been obtained from a sample water analysis: COD: 400 mg OzL" BODs: 300 mg OL! Dry residue at 105 C: 150 mg Fixed residue at 525 C: 130 mgl. Answer the following questions: A) What types of solids has it? B) Are they mainly organic or inorganic? C) What kinds of pollutants predominate in the sample? D) Is the organic matter biodegradable? E) Could we use it as drinking water? (Solution: B) Inorganic solids; C) Organic matter; D) Biodegradable organic matter is predominant; E) It could not use as drinking water.)