In the quadrilateral, ABCD, AB = r, BC = s, CD = t and DA = u

which of the following statements is true?

A.) r+s = t+ u

B.) r + s = t - u

C.) r - s = t - u

D.) r + s = -t - u

E.) r - s = u - t

my answer was A, but the book says its D

another question when subtracting vectors, do you just change the arrowhead of the negative vector of do you move the entire arrow to face the other direction?

2.) If m = 3i - 2j and n = i + j

a.) show that 2m + 4n is parallel to the x-axis

i know how to do the substitution bit, but how do i show that it is parallel

thanks alot guys