#### Answer

7

#### Work Step by Step

We are given that $f(x)=\sqrt(x+2)$ is a one-to-one function.
Also we know that the inverse of a one-to-one function $f$ is the one-to-one function $f^{-1}$ that consists of the set of all ordered pairs $(y,x)$ where $(x,y)$ belongs to $f$.
From 15a, we know that $f(7)=3$, which means that $f$ consists of the ordered pair $(7,3)$. Therefore, (3,7) must be a part of $f^{-1}$. Therefore, $f^{-1}(3)=7$.