What concentration of F- is necessary to start he precipitation of SrF2 from a saturated solution of SrSo4?
Ksp of SrF2 is 7.9*10^-10
Ksp of SrSO4 is 7.6*10^-7
I do not know how to show the working for this question

Very nice exersise
you have 2 equations and 2 unknows. Think about it