135. Solving a chemistry problem

7. A weighed portion of 1 g of metal containing tin was dissolved in acid and the solution was diluted with water to 100 ml. Five samples of 10.0 ml each were taken from the resulting solution, of which, after treatment with dithiol, 25 ml of colored solutions were obtained, the optical density of which was 0.32; 0.35; 0.30; 0.31; 0.33. To prepare a standard solution, 1 g of metal containing 4.56% tin was dissolved and processed under the same conditions.
The optical density of the resulting solutions was 0.20; 0.23; 0.23; 0.21; 0.24.
Determine the content of tin in the metal (in%) and the error of determination.