What is the percentage of the USA actors that showed up in the credit list of movie "Mrs. Doubtfire"?
USA actors refers to Birth Country = 'USA'; movie "Mrs. Doubtfire" refers to Title = 'Mrs. Doubtfire'; percentage = divide(count(ActorID where Birth Country = 'USA'), count(ActorID)) * 100%
SELECT CAST(SUM(CASE WHEN T3.`Birth Country` = 'USA' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T3.`Birth Country`) FROM movie AS T1 INNER JOIN characters AS T2 ON T1.MovieID = T2.MovieID INNER JOIN actor AS T3 ON T3.ActorID = T2.ActorID WHERE T1.Title = 'Mrs. Doubtfire'