High schooler here that just recently found out about source transformations. I wanted to try it out on a previous circuit we did using the good ol' KCL/KVL/Node/Mesh methods, but somehow, it gave me a different result. The circuit on the top is the original set up, with the voltage measured at R3 being -3.75V (correct answer). However, doing a source transformation around V1 and R2 results in the voltage at R3 changing to 24.5V!
I am stumped and may need an explanation on why the voltage changed when the source transformation technique was done properly. Or perhaps my technique was actually done improperly?