Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_68 ( goals_against INTEGER, goals_for VARCHAR, goal_difference VARCHAR )

### Question ###
What is the average of goals against, where overall goals are more than 35 and the goal difference is 20?

### Accurate SQL ###

SELECT AVG(goals_against) FROM table_name_68 WHERE goals_for > 35 AND goal_difference = 20