\(\frac{3}{x+1}-\frac{2}{x+3}=\frac{4x+5}{x^2+4x+3}\)
\(\Leftrightarrow\frac{3}{x+1}-\frac{2}{x+3}=\frac{4x+5}{\left(x+1\right)\left(x+3\right)}\)
\(\Leftrightarrow3\left(x+3\right)-2\left(x+1\right)=4x+5\)
\(\Leftrightarrow x+7=4x+5\)
\(\Leftrightarrow7=4x+5-x\)
\(\Leftrightarrow7=3x+5\)
\(\Leftrightarrow7-5=3x\)
\(\Leftrightarrow2=3x\)
\(\Leftrightarrow\frac{2}{3}=x\)
\(\Rightarrow x=\frac{2}{3}\)