NaCl+CaS=Na^2S+CaCl^2 balance

2NaCl + CaS - -> Na₂S + CaCl₂

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!