For what value of kkk does the matrix A=[12324k−1−20]A = \begin{bmatrix} 1 & 2 & 3 \\ 2 & 4 & k \\ -1 & -2 & 0 \end{bmatrix}A=12−124−23k0 have rank 2 (exactly two pivots)?
k=6k = 6k=6
k=5k = 5k=5
k=7k = 7k=7
k=−6k = -6k=−6