Substitute 7 into the equation.

$\begin{array}{l} g\left(7\right) = \sqrt{7 - 3} + 1 \\ g\left(7\right) = \sqrt{4} + 1 \\ g\left(7\right) = 2 + 1 \end{array}$

$g\left(7\right) = 3$

$g\left(4\right)=2$

Can you take the square root of a negative number?