CREATE TABLE table_35318 ("Player" TEXT, "Attempts" FLOAT, "Net yards" FLOAT, "Yards per attempt" FLOAT, "Touchdowns" FLOAT)

How many yards per attempt have net yards greater than 631?
SELECT SUM("Yards per attempt") FROM table_35318 WHERE "Net yards" > '631'
SELECT SUM("Yards per attempt") FROM "table_35318" WHERE "Net yards" > '631'