Hello there! I'm in some urgent need of some help to subtract vectors.

I can't seem to find out how to subtract them, I checked the sparknotes help page,

SparkNotes: SAT Physics: Vector Subtraction and tried it out with a question, but i can't seem to be getting the right answer.

And I've also been told of a tail-to-tail method approach which i don't seem to understand as well. If anyone has any decent sites / explanations they can provide, it would be great.

If you are interested in the question it's PQRS is a rectangle and PQ - RQ = PS - RS (all sides are vectors). Thank you!!