16. Solving a chemistry problem

3. Limestone weighed 0.0850 g was dissolved in 40 ml of HCl solution with Т=0.003645 g/ml in a volumetric flask with a capacity of 100 ml and the volume of the solution was brought to the mark. For titration of 20 ml of the resulting solution, 10 ml of 0.05 M NaOH solution was used. Calculate the content in (%) of CaCO3 in limestone.