1. **State the problem:** We have a function $f(x) = x + 2$ and its inverse $f^{-1}$. We are given that $f^{-1}(n) = 4$ and need to find the value of $n$. 2. **Recall the definition of inverse function:** The inverse function $f^{-1}$ reverses the effect of $f$. This means if $f^{-1}(n) = 4$, then $f(4) = n$. 3. **Calculate $f(4)$:** Using the function $f(x) = x + 2$, substitute $x = 4$: $$f(4) = 4 + 2 = 6$$ 4. **Conclusion:** Since $f(4) = n$, we have $n = 6$. **Final answer:** $\boxed{6}$ which corresponds to option D.