Answer:
2NaCl + CaS --> Na₂S + CaCl₂
Step-by-step explanation:
To balance a chemical equation there has to be the same number of products as reactants
NaCl + CaS --> Na₂S + CaCl₂
Since there are 2 Cl's and 2 Na's in the products (right side) there has to be 2 Na's and Cl's in the reactants (left side)
2NaCl + CaS --> Na₂S + CaCl₂
Now there is 2 Na's and 2 Cl's on each side and it is balanced!