Polygons

How many vertices does a convex polygon have, if the arithmetic mean of its interior angles is $140$?

The picture shows an intersection of two streets. Two water carts passed the intersection while sprinkling entire surface of the street. Each of the carts continued along the street it came. Determine how many square meters of the streets surface were sprinkled twice?

Let $ABCD$ be a parallelogram with $|AB|=8\mathrm{cm}$, $|BC|=3\mathrm{cm}$ and the measure of $\measuredangle DAB$ is ${30}^{\circ }$. Give the area of the parallelogram.

In the kite $ABCD$, $|AB|=|BC|=12\mathrm{cm}$, $|CD|=|DA|=6\mathrm{cm}$, and the measure of $\measuredangle DAB$ is ${120}^{\circ }$. Calculate the area of the kite.