Problem of midpoint theorem

In triangle $ABC$ , $D$ is the midpoint of $BC$ . $M$ is the midpoint of $AD$ . The extension of $BM$ intersects $AC$ at $F$ . If $AF=12$ , find $CF$ .

Hint: Midpoint theorem states that the segment connecting the midpoints of any two sides of a triangle is half the length of and parallel to the third side.