Vectors consist of magnitude and direction.
They can be both added and subtracted, to add a vector you place the vector you want to add onto the head of the first one. Addition is commutative (3 + 6 = 9 and 6 + 3 = 9 too) so can be done either way.
To subtract a vector, you reverse the direction of the vector you want to subtract. Subtraction is non-commutative (3 - 6 = -3 but 6 - 3 = 3) so you have to do it in the correct order.
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