From the photograph, the x axis is left-to-right and the y-axis is front-to-back. The range of values is -3<x<+2, and -2<y<+3. This gives a vertical range of z from -37 (front left) to +28 (front right).
Solutions of the partial derivatives gives horizontal planes where x^2-y=0, so at coordinates (-1,1) and (0,0). Second partials test shows that the point (-1,1) is a local maximum and (0,0) is a saddle, which can both be seen clearly on this model.
In case you hadn't guessed, my son is in the middle of Math102...
The print was created in openscad, scaled to 50x50mm base, and then the formula on the front was added in Sketchup.