How many students at the university earned a score of 90 in 2011?
in 2011 refers to year 2011; earned a score of 90 refers to score = 90;
SELECT COUNT(*) FROM university_year AS T1 INNER JOIN university_ranking_year AS T2 ON T1.university_id = T2.university_id WHERE T2.score = 90 AND T1.year = 2011