if there'e an internal hinge, then it's a determinate beam...but do not use Macaulay bracket functions...instead, use the basi double integration method
when yoy use Macaulay bracket functions, the condition is: if the value inside the pointed bracket is NEGATIVE, neglect the term... you can search google about it...
In the video, the detailed solution was not shown because I said that the reactions can be obtained using a calculator which has functions that can solve simultaneous equations. But if you want to solve it manually, you can use method of eliminations.