CREATE TABLE table_50159 ("Outcome" TEXT, "Date" TEXT, "Tournament" TEXT, "Surface" TEXT, "Partner" TEXT, "Opponents" TEXT, "Score" TEXT)

On what Surface was the match with a Score of 6 4, 6 3 and Runner-up Outcome played?
SELECT "Surface" FROM table_50159 WHERE "Outcome" = 'runner-up' AND "Score" = '6–4, 6–3'
SELECT "Surface" FROM "table_50159" WHERE "Outcome" = 'runner-up' AND "Score" = '6–4, 6–3'