Final answer:
In formal letters, use 'St.' for Street in the inside address and spell out street words. For U.S. addresses, spell out state names or use USPS abbreviations consistently.
Explanation:
The abbreviation that is appropriate to use in the inside address of a formal letter for Street is 'St.'. When typing mailing addresses, it's important to spell out street words like 'avenue' or 'street'. Additionally, when addressing someone in the U.S., spell out the state name or use the USPS abbreviation for the state consistently.
Learn more about Abbreviations in formal addresses here:
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