CREATE TABLE table_58647 ("Season" FLOAT, "Date" TEXT, "Winning Driver" TEXT, "Car #" FLOAT, "Sponsor" TEXT, "Make" TEXT, "Distance" TEXT, "Avg Speed" TEXT, "Margin of Victory" TEXT)

Who sponsored Greg Biffle's win on April 14?
SELECT "Sponsor" FROM table_58647 WHERE "Winning Driver" = 'greg biffle' AND "Date" = 'april 14'
SELECT "Sponsor" FROM "table_58647" WHERE "Date" = 'april 14' AND "Winning Driver" = 'greg biffle'