Let
$$f(x,y) = \begin{cases}
\frac{\sqrt{x} - \sqrt{y + 2}}{x - y - 2}, \text{ if } (x,y) \neq (4,2) \\
m, \text{ if } (x,y) = (4,2)
\end{cases}$$
For which value of the real number $m$ the function $f(x,y)$ is continuous at the point $(4,2)$?
Select one:
a. 1
b. $\frac{1}{4}$
c. $\frac{1}{2}$
d. $\frac{1}{5}$
e. 0