[ Measurement of segment lengths and angle measures. Adjacent angles.]

On a straight line, points $A, B, C$ and $D$ are marked sequentially, and $A B=B C=C D=6$.

Find the distance between the midpoints of segments $A B$ and $C D$.

#
Let $M$ and $N$ be the midpoints of segments $AB$ and $CD$ respectively. Then $MN = MB + BC + CN = 3 + 6 + 3 = 12$.

## Answer

12.