CREATE TABLE table_55415 ("Edition" TEXT, "Round" TEXT, "Date" TEXT, "Surface" TEXT, "Opponent" TEXT, "Result" TEXT)

On July 15, 1984 what surface was used?
SELECT "Surface" FROM table_55415 WHERE "Date" = 'july 15, 1984'
SELECT "Surface" FROM "table_55415" WHERE "Date" = 'july 15, 1984'