How do I complete problems 18, 20, and 22?

In problems 16 -25 , find all critical points and local extremes of each function on the given intervals. 16. f(x) = x"- 6x + 5 on the entire real number line. 17. f(x) = x - 6x +5 on [-2.5]. 18. f(x) = 2 - x on the entire real number line. 19. f(x) = 2- x* on [-2. 1] . 20. f(x) = x - 3x + 5 on the entire real number line. 21. f(x) = x - 3x +5 on [-2, 1] . 22. f(x) = x" - 5x#+ 5x+ 7 on the entire real number line. 23. f(x ) = x3- 5x#+ 5x-+ 7 on [0.2] . 24. f(x) = on the entire real number line. 25. f(x) = on [ 1. 3] . X + 1 2