What is the sum of the given expression?

$$\frac{x-2}{3x}+\frac{2x-4}{3x}$$

What is the difference of the expression below?

$$\frac{n^2-5}{4n^2-4}-\frac{n-3}{4n^2-4}$$

What is the LCD of the following expressions:

$$\frac{1}{8u^2v},\ \frac{u-v}{12uv^3},\ \frac{2u^2-1}{18u^3v^2}$$

What is the LCD of the following expressions:

$$\frac{2c}{c-1},\frac{c-2}{1-c^2}$$

What is the sum of the expression below?

$$\frac{1-b}{2b^2}+\frac{2}{3b}$$

What is the difference of the expression below?

$$\frac{2m}{2m-1}-\frac{5-m}{2m^2+7m-4}$$

Simplify the expression below:
$$-\frac{4}{x+2}+\frac{3}{x-1}-\frac{12}{x^2+x-2}$$