U can write 4 as 4/1 because 4/1 = 4
But since u got a mixed number with different dividents you have to get the same dividents.
The one from 4/5 is 5 and the one from 4/1 is 1.
SInce you have 4/1 you have to take both times 5 to get it to the same divident.
So 4/1 becomes 20/5.
20/5+ 4/5 is 24/5
24/5 is then 4.8
Other way around:
U take 4/5 and add it up to the 4
4/5= 0.8
4+ 0.8 = 4.8