[tex]\displaystyle\\
\frac{15}{x^2+4x}= \frac{^{3/}5}{4} \\\\
\frac{15}{x^2+4x}= \frac{15}{12} \\\\
\Longrightarrow~~x^2+4x = 12\\\\
x^2+4x - 12=0\\\\
x_{12}= \frac{-b\pm \sqrt{b^2-4ac} }{2a}= \frac{-4\pm \sqrt{16+48} }{2}=
\frac{-4\pm \sqrt{64} }{2}= {\bf \frac{-4\pm 8 }{2}}\\\\
x_1 = \frac{-4+ 8 }{2} = \frac{4 }{2} = \boxed{\bf 2}\\\\
x_2 = \frac{-4- 8 }{2} = \frac{-12 }{2} = \boxed{\bf -6}\\\\
[/tex]
