Answer:
radius cation/radius anion=a number and then get 0.40217. which is in the range for a 4 coordination number
Explanation:
https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Book%3A_Introduction_to_Inorganic_Chemistry/09%3A_Ionic_and_Covalent_Solids_-_Energetics/9.01%3A_Ionic_Radii_and_Radius_Ratios