1.

$OMA,ONB$ and $ABC$are straight lines.
$M$ is the midpoint of $OA$.
$B$ is the midpoint of $AC$.

$\overset{\rightarrow}{OA}=6a\overset{\rightarrow}{OB}=6b\overset{\rightarrow}{ON}=kb$ where $k$ is a scalar quantity.

Given that $MNC$is a straight line, find the value of $k$.