How many grams of sucrose must be dissolved in 250 ml to prepare the 0.15 mol / L solution?

How could you prepare 250 mL of 0.20M NaCl using only a solution of 1.0M NaCl and water? To prepare a 250 mL 0.20 M NaCl solution, I would place 50 mL of the 1.0 stock solution to a 250 mL volumetric flask and then add 200 mL of water. A bottle of the antiseptic hydrogen peroxide (H2O2) is labeled 3.0% (v/v).

- decrease the number of plants and animals living in the water.