Réponse:
1) Zach wrote the letter .
2) The letter was written because Zach missed his parents 3) He writted it while being in Exeter more precisely in a dormitory with other boys . A dormitory is composed by many mini studios , where in each one around 3 people live in.
4)The advantages are that it's possible to meet new friends , on the other hand the cons are many such as the food , the laundry only gets washed once per week and there's no place to hang the washed clothes . Moreover one of the cons is that they are far of they're family so you miss your family which is sad