Final answer:
The correct form of the verb 'ser' to use with the subject 'Miguel y Ud.' is 'sois'.
Step-by-step explanation:
If your subject was Miguel y Ud., the correct form of the verb ser to use would be sois.
In Spanish, ser is a verb that means 'to be' and it is used to indicate characteristics, professions, and origins. When the subject is 'Miguel y Ud.' (you and Miguel), the correct form of the verb is sois, which is the second-person plural form of the verb.
For example, you could say 'Miguel y ustedes sois estudiantes' (Miguel and you all are students) to indicate that both Miguel and the person being addressed are students.
Learn more about Verb conjugation in Spanish