How many 'number of seasons in top division' were played if the 'first season in top division' games is in 1990-91?
create table table_18143210_2 (number_of_seasons_in_top_division integer, first_season_in_top_division varchar, PRIMARY KEY (number_of_seasons_in_top_division))
select max(number_of_seasons_in_top_division) from table_18143210_2 where first_season_in_top_division = "1990-91"