I think the model showed at 32:00 slide, is not enough Mathematically supported, in two point. First, as a student indicated, this model has a threatens of Multi-Collonearity, becasue the right hand side has two term mapped from single "Fixed" variable X-vec, If you want to call your self "助教授" in stead of "助教", you have to explain more about the right term. Second, the right hand side terms has different units, and this doesn't support model reliability, without showing why that works.