Optimal solution of $\max f(x)$ subject to $g(x)\geq 0, x\geq 0$, $x \in \mathbb{R}^n$

Question

What can we say about the optimal solution (if exists) of the following nonlinear programming: $\max f(x)$ subject to $g(x)\geq 0, x\geq 0$, $x \in \mathbb{R}^n$ and functions $f,g: \mathbb{R}^n \to \mathbb{R}_+$ is differentiable and bounded.

I have no idea on finding the optimal solution. Can anyone give me some hints? Thank you in advance!