You are close, but the statement needs some adjustments. Here's why:

* You need 40 grams of calcium and 32 grams of sulfur to make 72 grams of calcium sulfide (CaS).

Let's break it down:

* Calcium (Ca) has an atomic mass of 40 g/mol.

* Sulfur (S) has an atomic mass of 32 g/mol.

* Calcium sulfide (CaS) is formed by the reaction of one calcium atom with one sulfur atom.

Therefore:

* The mass of one mole of CaS is 40 g/mol (Ca) + 32 g/mol (S) = 72 g/mol.

So, to make 72 grams of calcium sulfide, you need 40 grams of calcium and 32 grams of sulfur. This is based on the law of conservation of mass, which states that matter cannot be created or destroyed, only transformed.