The Domain of the function are the set of x values of the graph. So, assuming this is the whole graph (that it doesn't continueof screen), the Domain will be the set from the lowest "x" value to the highest. The lowest is the leftmost, which is, in this case, 0, and the highest is the rightmost, which is in the 8th tick, and, since the graph is counting by two on "x", this is x = 16.
These poinst are included, so the domain is:
The range is similar, but for the "y" values. So, the lowest is y = 0 and the highest is on the 4th tick, since it is counting by 20 on "y", this is y = 80. So, the Range is:
To check if it is a function, we need to check if each x values correspond to a single y value. We can do it by checking if there is any vertical line that passes through the graph 2 or more times. But, since it is a line, this won't happen, which means each "x" have only one corresponding "y" so this it a function.
A discrete function don't complete every point of "x", it "jumps" and in at least one part of the graph. But this graph don't have any "jumps", it continue from start to end without undefined values, so it is continuous.