K=2
1) Considering that B is the image of dilated A, then we can state that there was an enlargement of triangle A, so k (Dilation factor) is definitely > 1.
2) When we examine the vertices of A and B we can state:
A( -2,-3) A' (-4,6)
B(-5,-3) B' (-10,-6)
C( -1, -6) C' (-2,-12)
3) As we can notice, each coordinate of A'B'C' is twice ABC. So we can state that the Scale Factor is k =2