Answer:
4 if x < 3
Explanation:
First, find the equation of the line. From the graph we can tell the y-intercept is 4 and the slope is 0. Using y=mx+b, we find that y=(0)x+4 (same as y=4). f(x) is the same as y, so all you have to write is 4.
To find the domain, you must look at where the function is defined. It is only defined to the left of the point (3,4), where x < 3. We know its only defined there because the arrow and line only go in that direction. We know that it should be a < not a ≤ because the point at (3,4) is hollow, so (3,4) is not a point in the function and not included in the domain.