How do I solve this problem on the concentration of fluorine

Question

If a constant  [F-] is maintained in a solution in which the initial  [Ca2+ ] =0.038M, what percentage of Ca 2+ will remain in solution after the CaF2 precipitate. What [F-] should be maintained to ensure that only 3.4% of the Ca 2+ remains unprecipitated?

Answer 1

CaF₂(s) <==> Ca²⁺(aq) + 2F^-(aq)

Ksp = [Ca₂₊][F^-]²

Look up the Ksp and use it and 0.038 for [Ca²⁺] and solve for [F^-].  Use that to determine moles CaF₂ precipitated since 2 moles F^- = 1 moles CaF₂.  Then determine %Ca²⁺ remaining in solution.