36. Solving a chemistry problem

9. a) What volume of hydrochloric acid with a mass fraction of 21.36% and a density of 1.105 g / cm3 must be taken per 20 dm3 of water so that 1 cm3 of the resulting solution contains 0.002136 g of HCl? Specify the method of preparation of the solution.
b) What sample of chemically pure potassium chloride must be taken to prepare 2 dm3 of a solution with a molar concentration of equivalents of 0.5010 mol / dm3? With what accuracy should the sample be calculated and on what scales should it be weighed?