Vector a with arrow has a magnitude of 12.2 units and points due west. vector b with arrow points due north. (a) what is the magnitude of b with arrow if a with arrow + b with arrow has a magnitude of 17.4 units? 21.2 incorrect: your answer is incorrect. units (b) what is the direction of a with arrow + b with arrow relative to due west? ° correct: your answer is correct. (c) what is the magnitude of b with arrow if a with arrow â b with arrow has a magnitude of 17.4 units? units (d) what is the direction of a with arrow â b with arrow relative to due west? ° correct: your answer is correct.