Answer: D. g(x) = f(x)+4
The graph shows f(x) to have a y intercept at -1, which is where the diagonal line crosses the y axis. We want the y intercept to move to 3. So we must add 4 to the old y intercept to get the new y intercept.
We do this with every single point on f(x) to get g(x) = f(x)+4. This shifts the graph up 4 units.