Hi !!
The correct answer is "tu es sympa"
For the other ones, it should have been so :
Les garçons sont petits (garçons = masculine plural, so the verb is 3rd person and the adjective M.P
La fille a seize ans = (the girl is sixteen = "have" instead of "be" and always "ans" after the number)
La classe est intéressante = ("la classe" is feminine singular, the verb is ok but the adjective stayed in masculine = intéressant, has to be feminine as the subject, it's "la classe " which is "intéressante", so they have to agree together)
hope I helped !!
