CREATE TABLE table_name_13 (score VARCHAR2, country VARCHAR2, player VARCHAR2)

What is Score, when Country is 'United States', and when Player is 'John Mahaffey'?
SELECT score FROM table_name_13 WHERE country = "united states" AND player = "john mahaffey"
SELECT "score" FROM "table_name_13" WHERE "country" = "united states" AND "john mahaffey" = "player"