Answer:
formal
Explanation:
'strict' and 'harsh' are out because business letters are not meant to insult or criticise, but rather to be courteous (polite). 'fancy' is out because business letters do not use unnecessarily flowery language.
as such, that only leaves us with 'formal' which is an appropriate tone for a business letter since it conveys a sense of seriousness.
i hope this helps! :D
