7. Solving a chemistry problem

5. The relative optical density of a standard solution containing 35 mg/l of anthracene at λ=253 nm is 0.412. For the test solution, this value is 0.396. In the comparison cuvette in both cases there was a solution containing 30.0 mg/l of anthracene. Calculate the concentration (mg/l) of anthracene in the test solution.