1. Points A, B and C have position vectors $\overset{\rightarrow}{OA}=-6i-2j$,  $\overset{\rightarrow}{OB}=i+mj$and  $\overset{\rightarrow}{OC}=3i-8j$, respectively.

Given that A, B and C lie on the same straight line, use a vector method to find the value of m.