Adding Angles

The six marked angles are all the angles at the five vertices in the diagram, except for those that are the interior angles of the two triangles.

There are $360^\circ$ at each vertex he total of all the angles at the five vertices is $5 \times 360^\circ = 1800^\circ$.

There are two triangles, each of which has interior angles that add up to $180^\circ$. Therefore the total angle is $2 \times 180^\circ = 360^\circ$.

The marked angles are all the rest of the angles, so total $1800^\circ - 360^\circ = 1440^\circ$.