interests creating

Smith owned Black acre in fee simple absolute. In section 3 of a properly executed will, Smith devised Black acre as follows: “I devise my farm Black acre to my son Darwin so long as it is used as a farm.” Sections 5 and 6 of the will made gifts to persons other than Darwin. The last clause of Smith’s will provided: “All the remainder of my real and personal property not disposed of heretofore in this will, I devise and bequeath to Stanford University.”
Smith died in 2009, survived by her son Darwin. Smith’s estate has been administered. Darwin has been offered $100,000 for Black acre if he can convey title to it in fee simple. What interests in Black acre were created by Smith’s will?