Nunc laetus es, sed nuper non laetus eras. Cur miser eras?
Key: Now you are happy, but recently you weren’t happy. Why were you sad?
I don't have "sad" as a meaning for misera; wretched, unfortunate. Is there another definition someplace that I missed?
Nunc sum apud socios meos.
Nunc laeti sumus et erimus.
Now I am with my companions. Should be among.
Now I am and will be happy. Should be plural, We are happy and we will be (happy)
The teachers were happy because of the boys industry.
Key: Magistri erant laeti industria puerorum.
The word I have for "industry" is diligentia, -ae. I think this is the ablative of cause, in the plural: diligentiis. This is another case where I'm not sure of the use of of word that can be applied to an individual or a group; an attribute of one or many. What would be the use of the word in the plural? Industries? I've just keyed on to whom the attribute is applied (the boys) and followed that. I infer from the word "industria" that it is singular, though.