How can I calculate the mass percent of free Cl- in these problems?

How can I calculate the mass percent of free Cl- in these problems?
Gravimetric analysis using Ag+: From the mass of dry AgCl to mass% of free Cl-
Volumetric Analysis using Hg2+: From the volume of the standardized used to mass% of free Cl-
Spectrophotometry : construct a Beer’s Law plot form the standard solution of Co2+, calculate %mass cobalt