Hi there!
A function is a special type of relation where we only get 1 y-value for every value of x.
Notice how in the set, for the x-value of 4, we're getting both -7 and 7. This means this is NOT a function.
The domain is the possible x-values, and the range is the possible y-values:
Domain: {-4, 4, 5, 6}
Range: {-8, -7, 6, 7, 8}
I hope this helps!