a: \(=\dfrac{x+3-x-4}{x-2}=\dfrac{-1}{x-2}\)
b: \(=\dfrac{x^2+x+4x+6}{2x\left(x+3\right)}=\dfrac{\left(x+3\right)\left(x+2\right)}{2x\left(x+3\right)}=\dfrac{x+2}{2x}\)
c: \(=\dfrac{3x-x+6}{x\left(2x+6\right)}=\dfrac{2x+6}{x\left(2x+6\right)}=\dfrac{1}{x}\)
d: \(=\dfrac{2\left(x+3\right)}{x\left(3x-1\right)}\cdot\dfrac{-\left(3x-1\right)}{x\left(x+3\right)}=\dfrac{-2}{x^2}\)
h: \(=\dfrac{x^2-x^2-2x-2x+4}{\left(x-2\right)\left(x+2\right)}=\dfrac{-4x+4}{\left(x-2\right)\left(x+2\right)}\)