Robert knows it is important for him to dress appropriately and make sure his hair is neatly trimmed when he goes for an interview because the employer will expect him to do so. This example of a social convention is called a

Folkway.

Explanation:

Folkways as defined by  William Graham Sumner refers to the norms deriving from and organizing casual interactions and emerging from repetition and routines.  people indulge in them to meet our everyday needs, and they are most often operationally unconscious, while they are very helpful for the orderly operation of society. In society, a well-dressed individual is much admired. Most well-known celebrities are praised for their dressing sense, especially politicians and celebrities. Clothes represent the personality of each individual. as per the question, Robert is expected in a certain way by his employers is an example of folkway.

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