Roger the Shrubber, a recent acquaintance who has considerable expertise in the arrangement, design and sale of shrubberies, has specified 500 feet of picket fencing for this particular design. (Plus, picket fencing is on sale this week at Home Depot in 10 foot lengths in time for the next holiday weekend.) Arthur and his knight decide to maximize the effect of their sacrifice by enclosing the greatest area of a rectangle possible. What is the greatest area possible using this amount of fencing?