Find value if S, E and B are collinear

[natasha.ch]

In triangle OAB, C is a point on OB such that OC=3CB. S is a point on OA such that OS=4SA. E is a point on AC such that AE=λEC. Given that [tex]\vec{OA}[/tex]=5p and [tex]\vec{OB}[/tex]=4q, Find value of λ if S, E and B are collinear.