Question was solve

These three problems have already been solved by my teacher however, I do not understand the entire question was solved. For example (real example) how did my teacher find variable “s”? Also please fully elaborate the test calculation (I don’t understand this at all) so I can fully understand how each step was done.

This is actual tutor help and I need it to be completed within the next hour/3 hour tops

This is to help me take my exam this evening (berlin time zone)