The formula for a slope of line going through two coordinates is: (y2 - y1)/(x2 - x1).
Label your two sets of coordinates (3, 4) as (x1, y1) and (0, 2) as (x2, y2) and plug those into the slope formula:
(2 - 4)/(0 -3) = -2/-3 = 2/3 final answer