#### Answer

LCD=(x-1)(x+1)(3x+1)(4x+1)

#### Work Step by Step

$\frac{3x}{4x^{2}+5x+1}$, $\frac{5}{3x^{2}-2x-1}$
4$x^{2}$+5x+1=4$x^{2}$+x+4x+1=x(4x+1)+1(4x+1)=(x+1)(4x+1)
3$x^{2}$-2x-1=3$x^{2}$+x-3x-1=x(3x+1)-1(3x+1)=(x-1)(3x+1)
LCD=(x-1)(x+1)(3x+1)(4x+1)