Please help me this question. Thanks in advance.

Shelly needs $3,500 to buy equipment for her new business. Ted agrees to loan Shelly $3,500, accepting as collateral Shelly's car. They put their agreement in writing and sign it. Shelly keeps possession of the car. Does Ted have an enforceable security interest? How can Ted let other creditors know of his interest in the car? Fully explain your answer.