I'm having difficulties solving the following problems, I would very much appreciate it if someone could show me how to solve them step-by-step.

Add or Subtract as indicated and simplify.

14. (x)/(x +3) + (3)/(x +3)

15. (a^2 - 1)/(a - 1) - (a - 1)/(a + 1)

16. (1)/(x) - (3)/(x+2) - (6)/(x^2 + 2x)

Multiply or divide as indicated and simplify.

17. (x^2 + x - 20)/(x^2 - 16) times (x^2 - 25)/(x - 5)

18. (x + 2)/(x^2 + 2x + 1) divided by (x^2 - 4)/(x + 1)