Final answer:
The appropriate form of the verb estar to fill in the blank in the sentence is estás.
Step-by-step explanation:
The appropriate form of the verb estar to fill in the blank in the sentence is estás. The sentence would read, "Estás en la clase de inglés con Juan, ¿no?".
The verb estar is used to indicate location or temporary states, and the form of the verb depends on the subject. In this case, since the subject is tú (you), the appropriate form is estás.
For example, to express "I am" you would use estoy, and to express "he/she/it is" you would use está.
Learn more about Verb conjugation in Spanish