Rational: Any number that can be expressed as a fraction (or a ratio.)
Irrational: Not rational, any number that can't be written down as a fraction. Some examples include

,

, and so on.
Pretty sure its the 3rd one
-- Find how much 'y' changes from the first point to the second one.
-- Find how much 'x' changes from the first point to the second one.
-- The slope of the line going from the first point to the second one is
(change in 'y') / (change in 'x') .