Question

How do I calculate the amounts of Na2SO4 and CaCl2 that I need to create a solution of CaSO4 at 9 grams/Liter concentration?

Answer 1

CaCl2 + Na2SO4 ==> CaSO4 + 2NaCl

9 g CaSO4 is how many mols? That's 9/molar mass CaSO4 = approx 0.066 but you need an accurate answer.
Then 0.066 mols CaSO4 will require 0.066 mols Na2SO4 and 0.066 mols CaCl2.
g CaCl2 = mols x molar mass = ?
g Na2SO4 = mols x molar mass = ?
Dissolve those amounts in 1 L, mix, and voila!