Area of Triangles · Superchallenge problem

Trapezoid $ABCD$ has $AB$ parallel to $DC$, with $AB = 14$ cm, $DC = 6$ cm and a height of $10$ cm. The two slanted sides are $BC$ and $AD$. Point $M$ is the midpoint of $BC$. What is the area of triangle $AMD$, in square centimeters?