CREATE TABLE table_45928 ("Outcome" TEXT, "Year" FLOAT, "Championship" TEXT, "Surface" TEXT, "Opponent in the final" TEXT, "Score in the final" TEXT)

How many years have an Opponent in the final of welby van horn?
SELECT SUM("Year") FROM table_45928 WHERE "Opponent in the final" = 'welby van horn'
SELECT SUM("Year") FROM "table_45928" WHERE "Opponent in the final" = 'welby van horn'