Find the domain and range for each of the graphs in both inequality and interval notation

To find the domain and the range from the graph of a function, we consider perpendicular projections of the graph to the x-axis and to the y-axis.

The projection to the x-axis is the Domain (the orange line segments), and the projection to the y-axis gives us the Range (the yellow line segments).

20.

Domain: [-6, -1) ∪ (-1, 4]          Range: (-3, 5]

21

Domain: [-5, -2)∪(-2, 2)∪(2, 7]         Range:  [-3, 5]

22.

Domain (-5, 3],        Range: {1}

23.

Domain:   (-5, 4],       Range: [-3, 4]

(-4, 7).
You would negate, Change the sign, for both X and Y when reflecting over the y-axis.