Well, it looks like the curve starts from where the x- and y-axes meet? Are we meant to infer that this point is the origin (0,0)? If we are, then that gives a second point and makes proceeding easier. If that's not the case, you can still find a curve that fits the given information, just maybe not the one unique curve.
Just based on the shape of the graph, you (should) know it's going to have the basic form of y = -e^-x. Now that has a horizontal asymptote at y = 0, but the curve you want to find has a horizontal asymptote at y = 4. Can you adjust the equation so that's the case? Oh, but the curve still doesn't pass through the given point (1,2). What might you do to fix the equation so it does? As a hint, consider how the graphs of y = -e5-x and y = -e10-x differ. Also consider how the curves y = -7e-x and y = -3e-x differ.
Please share with us any and all work you've done on this problem, even including the parts you know for sure are wrong. Thank you.