CREATE TABLE table_54160 ("Outcome" TEXT, "Date" TEXT, "Tournament" TEXT, "Surface" TEXT, "Opponent in the final" TEXT, "Score in the final" TEXT)

What was the surface where the outcome was winner on 12 march 1989?
SELECT "Surface" FROM table_54160 WHERE "Outcome" = 'winner' AND "Date" = '12 march 1989'
SELECT "Surface" FROM "table_54160" WHERE "Date" = '12 march 1989' AND "Outcome" = 'winner'