1. **State the problem:** Given the expression $(h t u h) = 4 h u + 3 u$ and the term $(n + 3) 3$, we want to understand the restrictions on the variables. 2. **Identify the variables and expressions:** The expression involves variables $h$, $t$, $u$, and $n$. The term $(n + 3) 3$ is a product of $(n+3)$ and $3$. 3. **State restrictions:** - Since the expression involves multiplication and addition, all variables must be defined in a domain where these operations are valid (usually real numbers). - If any variable appears in a denominator or under a root (not shown here), restrictions would apply to avoid division by zero or negative roots. - Here, no denominators or roots are present, so no explicit restrictions from the expression itself. 4. **Conclusion:** The variables $h$, $t$, $u$, and $n$ can be any real numbers. There are no stated restrictions from the given expressions. **Final answer:** $$\text{Restrictions: } h, t, u, n \in \mathbb{R}$$