How to normalize a table that contains a CK not included in the PK? I have the following table. The PK is model_ID.
Assuming that the modelName field is unique(that is, no two brands can have an identical modelName), there is a transitive dependency between modelName and brand.

What is the optimal solution for the table to comply with 3NF, without having the modelName field as part of the PK?
Model name does not need to be part of the PK.  The problem with this table is brand. "Scott" is repeated. Model relies on Brand, but brand does not rely on model. 

Create a brand table. Turn the Model.brand to Brand_FK.