\[3 + \frac{a}{x + 5} = \frac{3x}{x + 5}\]
\[3^{\backslash x + 5} + \frac{a}{x + 5} = \frac{3x + 15 + a}{x + 5} =\]
\[= \frac{3x}{x + 5} \Longrightarrow a = - 15.\]