Mike signed and delivered a note for $9,000 to Paul Payee in exchange for Paul's tractor. Paul transferred the note to Hilda, who promised to pay $7,500 for it. After Hilda had paid Paul $5,000 of the promised $7,500, Hilda learned that Mike had a defense: the tractor was defective. How much, if anything, can Hilda collect from Mike on the note, and why?