Mention the properties of isosceles trapezium.

$ABC$ is a triangle in which the base $BC$ is $24 \mathrm{cm}$ and the altitude from $A$ to $BC$ is $20 \mathrm{cm}$. If the area of the triangle is $k {\mathrm{cm}}^2$, then find the value of $k$.

The sides of a triangle are $25 \mathrm{m}, 39 \mathrm{m}$ and $56 \mathrm{m}$. Find the area of the triangle and also the perpendicular distance from the vertex opposite to the side of length $56 \mathrm{m}$.