Ill give it a shot.
10 2/5 + 10 4/5 = 21 1/5
You’d add the whole numbers, and once you add the fractions, you get a whole number and the remaining fraction. 4+2 = 6, so you’d have 6/5, which gives you another whole number, and leaves you with 1/5. So subtract 21 1/5 from 25, and you’d get 4 4/5. My apologies if Im wrong.