1. **State the problem:** Simplify or understand the expression $$\frac{5+x}{12+x}$$. 2. **Formula and rules:** This is a rational expression, a fraction where numerator and denominator are polynomials. 3. **Check for simplification:** To simplify, factor numerator and denominator if possible. 4. **Factor numerator:** $5+x$ cannot be factored further (it is linear). 5. **Factor denominator:** $12+x$ also cannot be factored further (linear). 6. **No common factors:** Since numerator and denominator share no common factors, the expression is already in simplest form. 7. **Domain:** The expression is defined for all $x$ except where denominator is zero, so $x \neq -12$. **Final answer:** The expression $$\frac{5+x}{12+x}$$ is already simplified and defined for all $x \neq -12$.