An aqueous solution of sodium fluoride is slowly added to a water sample that contains barium ion (0.0400 M) and calcium ion (0.0630 M). The Ksp of barium fluoride is 1.00x10-6. The Ksp of calcium fluoride is 3.90x10-11. What is the remaining concentration of the first ion to precipitate when the second ion begins to precipitate? Number M