Let X[k] be the DFT of a real signal x[n] with 12 samples and assume that X[k] for k-0,1,...,6 is given by X[k] = { 12, -18-21i, -10+4i, -6+7i, 9+8i, 19-16i, 39), for 0 e) sum x[n] exp(j pi n/3) A) -10-4j B) -9+6j C) 2-5j D) 5+9j f) sum x[n]^2 A 426.75 D 500.65 C) 751.76 675.25