Training produces y=10+2x. For test x values 7 and 8, predictions 24 and 26 differ from actual 25 and 27 by one each. MAE improves from baseline 9 to model 1 on this tiny synthetic holdout only.

Critical check: Held-out targets never enter fitting and the baseline and model use the same evaluation rows.

Final project: Submit the data, runnable training/evaluation script, scatter plot, error table and model card. Add a separate challenge row x=9, y=35 without refitting and explain the resulting error and a possible distribution-shift concern.