2.
Unformal
May 29 Reveille at 2:15 am. Left for (shooting) ranges at 3 am, returned at 10 am. Left again for ranges with markers at 3 pm, returned at 9 pm, distance to ranges 2 miles. Food here is not very plentiful, not enough to live on. Getting fed up with this place. Same everyday till…
Formal
On May 29th William Falcus had Reveille at 2:15 a.m. He left for the shooting ranges at 3 a.m. and returned at 10 a.m. At 3 p.m. he left for the ranges again, this time with markers and returned at 9 p.m. The distance to the ranges was 2 miles. William Falcus felt that they did not get enough food to live on. He was unhappy that everything was always the same.
Theese are two texts have the same content but are not written in the same style. In the informal part you could use a sentence like "Getting fed up with this place. Same everyday till" this compared to "He was unhappy that everything was always the same", generally the formal writing use face saving, not expressing opinions without a "felt" or something else to soften up the message. "May 29" in the unformal text is transformed into "On May 29th" elongating the sentence with more correct writing. Generally in formal texts usage of slang and abbreviations is kept to a minimum but is and can be used in a unformal text.
3.
Formal
The word police has over the years been derived from an old expression meaning "man of the city". Usage of the term has over time given birth to slang words like copper, bacon and pig. Theese words are often said without men of the law present but some of the slangwords are more commonly accepted making usage allowed.
Informal
Police, or yah, men of the city. Ther's alot of good words for cops, pig, bacon and copper, of course you should be careful, using them when one is around could give you a headache. some of them are allowed to use but make damn sure you are sure you are in the right place and the right company!

Good job Axel!
SvaraRaderaYour definition of style is very good, but can be rephrased for clarity and flow. My suggestion:
"Style in academic writing is what writers use to create a certain feeling, appropriate to the context, in their text. In order to do so, they must choose the correct form, method and level of formality. ... Using style effectively means adapting the syntax, vocabulary and grammar of a text to the intended audience." (or something)
INformal (not unformal)
"THESE TWO texts have the same content but are not written in the same style. In the informal ONE THERE IS a sentence like... and this can be compared to... "
"Generally speaking, the formal writing USES face saving..."???("face-saving language"?)" I think this is simply because the informal text is written in the 1st person singular and the formal one in 3rd person, right?
"Generally in formal texts the USE of slang and abbreviations is kept to a minimum but this type of language can be used in AN INformal text."
Your own texts show very clearly that you know the difference between formal and informal writing. One typo: "These words are often said..."
Well done!
Anna