Easy, round them into whole numbers,
change them into whole numbers:
9 --->9
and
3 7/8 can be changed into 4. ( 3 7/8 is almost 3 8/8 --->4)
9-4=5
5 is your estimate.
Now,
9- 3 7/8
9 changes into 8 8/8 to be able to subtract
8 8/8
-
3 7/8
=
5 1/8
These are your answers. 5 and 5 1/8.
