Find the values of x(if any) at which f is not continuous and determine whether each such value is a removable discontinuity.

1. f(x) = x^2-4/x^3-8

2. f(x) = {2x-3, x is less than or equal to 2

x^2, x>2

3. f(x) = { 3x^2+5, x is not equal to 1

6, x=1

i dont really know where to start.i have read the book but can't really understand. someone help please.