Answer: You must rearange 3 3/4 into an improper fraction to make the subtraction easier.
Explanation:
(this is a little long bear with me :3)
3 and 3/4ths into a improper fraction would be: 15/4
looking at 15/4 and 7/8 notice how the denominators are 4, and 8. both are common denominators. so we multiply 4x2 to make 4, into 8. and whatever we do to the bottom, we do to the top.
15x2 30
---------- = ------
4x2 8
our new fraction is 30/8.
do the subtraction..
30 7 23
---- - --- = --- that then turns into a mixed number, which is:
8 8 8
2 7/8.
hope this helped! :)