a: \(=\dfrac{x^2+2x+1}{3\left(x+1\right)}=\dfrac{x+1}{3}\)
b: \(=\dfrac{3x+5+15x-5}{4x^3y}=\dfrac{18x}{4x^3y}=\dfrac{9}{2x^2y}\)
c: \(=\dfrac{x+1}{2\left(x-1\right)}-\dfrac{2x}{\left(x-1\right)\left(x+1\right)}\)
\(=\dfrac{x^2+2x+1-4x}{2\left(x-1\right)\left(x+1\right)}=\dfrac{\left(x-1\right)^2}{2\left(x-1\right)\left(x+1\right)}=\dfrac{x-1}{2x+2}\)