The domain is the set of possible inputs and the range is the set of possible outputs. This is a function because each input goes to exactly one output.
========================================
Problem 2
This is a function as well. We do not have any input going to multiple outputs.
Domain = {-2, -3, 5}
Range = {6, 7, 8}
========================================
Problem 3
This is not a function. The input -4 goes to more than one output (outputs 3 and -1 at the same time)