a function maps every element of it's domain to a single value in it's range.
the only completion of the first table is so that f is not a function is
-1 | anything but -8 |
-1 | 8 |
6 | anything |
Any other completion of this table will ensure f is a function.
For the second part.
-1 | anything but -8 |
-1 | -8 |
6 | anything |
is not a function because -1 is mapped to two different values