The formula of the coordination compound Tetraammineaquachloridocobalt (III) chloride is

Explanation

Anion (simple ion) `=Cl^(-)`
for the coordination entity, writing first the symbol for metal atom and then the ligands in the alphabetical order, we have
Cation (complex ion) `=[Co(NH_(3))_(4)(H_(2)O)Cl]^(x)` where x is the charge on the complex ion.
x = oxidation state to cobalt + charge on the ligands
x=+3+0+0+(-1)=+2
(`H_(2)O` and `NH_(3)` are neutral group and carry no charge. Only chlorido group carries charge = - 1)
Charge on one anion = - 1
Charge on complex cation = + 2
Clearly, two anions will neutralise the charge of the cation.
Hence, formula of the given compound is `[Co(NH_(3))_(4)(H_(2)O)Cl]Cl_(2)`.