Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_8 (goal_difference INTEGER, club VARCHAR)
### Question:
What is the average goal difference using slavia sofia club?
### Answer:
SELECT AVG(goal_difference) FROM table_name_8 WHERE club = "slavia sofia"