SMO 2019 Junior Round 1 Question 5

In a quadrilateral $ABCD$, the diagonals $AC$ and $BD$ intersect at the point $O$. Suppose that $\angle BAD+\angle ACB=180^\circ$, $|BC|=3$, $|AD|=4$, $|AC|=5$ and $|AB|=6$. What is the value of $\frac{|OD|}{|OB|}$?