Which is more formal?

tú
usted

Does anyone know what my spanish teacher means by this? i need to use plural forms of the verb ser. and she asked me to use a couple of adjectives to describe the boys collectively and then the girls collectively?

Fill in the blank with the correct form of the verb "tener" ellos muchos amigos

Realiza el análisis espacial del municipio de cuautitlan izcalli (utilisando las categorias de analisis)