I'm having trouble with the following commands

i. count the number of lines which end in a 4 letter word
grep '[a-z-A-Z]{4\}$' bfile <<seems to print out everything

abc abc abcd
joe joe john
bob bill
gregory greg
greg gregory

the grep command prints out the lines with 4 letter words and the line "greg gregory"

ii. count the number of lines that
contain a number larger than or equal to 100,
contain exactly 5 characters

iii. find all the files in a hierarchy which contain more than 25 characters

The way you have phrased your question would suggest that this a homework assignment. If this is the case, then you would have violated the forum rules.

They aren't homework questions per se, they're questions given in preparation for a test; so they aren't graded, but I guess ultimately you're the moderator and its your word against mine.

When your tutor gave you these questions I am sure that their intention was that you attempt to answer the problems on your own, rather than to post here in the hope that other people might answer them for you.
Try putting in the effort yourself and perhaps you might find that you retain the knowledge better and score higher.