Angle-Sum Property of a Quadrilateral

Consider a concave quadrilateral $\mathrm{ABCD}$. What is the sum of interior angles of a concave quadrilateral? Write the answer in degree $\left(°\right)$.

Check the following are trapeziums or not? Why?

The angles of a quadrilateral cannot be in the ratio $1:2:3:6$. Why? Give reasons.

In a quadrilateral, the angles are $x°, (x+10)°, \left(x+20\right)°, \left(x+30\right)°$. Find them.

The four angles of the quadrilateral are equal. Find each of them.

The angles of the quadrilateral are in the ratio $2:3:4:6$. Find the measure of each of the four angles.

The three angles of a quadrilateral are $60°, 80°$ and $120°$. If the fourth angle is $k°$, find $k$.