Hey there! I'm happy to help!
Let's call our fraction x.
x=3.777......
We want to get rid of the repeating stuff. If we multiply our fraction by 10, we get 10x=37.7777.
We see that if we subtract x from 10x, the repeating numbers will be cancelled out. Let's do this.
10x=37.7777
-
x=3.77777
=
9x=34
We divide both sides by 9.
x=34/9=3 7/9.
Have a wonderful day! :D