1. Let's clarify the problem: you asked why the expression $12g - 4h$ can become an addition. 2. The original expression $12g - 4h$ involves subtraction, not addition. However, subtraction can be rewritten as addition by using the negative sign. 3. Subtraction of $4h$ means adding the opposite of $4h$. 4. So, we rewrite: $$12g - 4h = 12g + (-4h)$$ 5. This shows that subtraction is the same as addition of the negative term. 6. This transformation is useful because it allows us to treat subtraction as addition, which can simplify algebraic manipulation.