There are two methods for subtracting one vector from another:
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(A) Using trigonometry formulas galore and more;
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(B) Using visual, graphic methods.
So if you are not friends with Trig Boy, then use this podcast. It covers the graphical no-trig method for subtracting two vectors. You could do it really nicely with pencil, graph paper, and straight edge.
If you look over pp. 38-40 in chapter 3, and pp. 58-59 in chapter 4, you will find supporting text and more diagrams, and especially chapter 4 exercises 1-6, on p. 73.