13. Five marks exercise problems VIII

Two line segments $\overline{AD}$ and $\overline{BC}$ intersect at $O$. Joining $\overline{AB}$ and $\overline{DC}$ we get two triangles, $\Delta AOB$ and $\Delta DOC$ as shown in the figure. Find the $\angle A$ and $\angle B$.

 

 

$A =$ $^\circ$

 

$B =$ $^\circ$