Complex sentence: The Gilbert Model focuses more on income when referring to how the economic system places people in classes; and income of a person is directly related to a person's educational preparation because better education provides for a better occupation which raises their class level.
Split into simpler sentences: The Gilbert model focuses more on income when referring to how the economic system places people in classes. The income of a person is directly related to a person's educational preparation because better education provides for a better occupation which in turn raises their class level.