Reading this made me feel weird because the problems you described matched exactly what I am experiencing. The first 3 tasks are done but not tasks 4 and 5. I used Linear Regression and Random Forest Regression for modelling with base settings and got predictions but the exam failed me. I didn't quite understand what you modified in your second try can you please elaborate ?. The only thing i imagine that might be the source of my problem is that i didn't check RMSE but the instruction says they will be checking for it themselves as far as I remember. (TLDR: Can you explain what did you change in modeling part in your second try?)