CREATE TABLE table_name_34 (duration VARCHAR, start VARCHAR, stage VARCHAR, difficulty VARCHAR)

How long does the one that stars with son bou of middle difficulty, and on a stage number larger than 13 last?
SELECT duration FROM table_name_34 WHERE stage > 13 AND difficulty = "middle" AND start = "son bou"
SELECT "duration" FROM "table_name_34" WHERE "difficulty" = "middle" AND "son bou" = "start" AND "stage" > 13