Find the area of shaded region.

In $△ABC, AD$ is the median and $G$ is a point on $AD$ such that $AG:GD=2:1$. Then area $(△BDG):$area $(△ABC)$ is equal to:

The three sides of a triangle are $15 cm, 36 cm, and 39 cm$ long. A small triangle is formed by joining the mid points of the three sides of this triangle. The area of small triangle will be_____ $c{m}^2$  

The hypotenuse of a right-angled triangle is $39 \mathrm{cm}$ and the difference of other two sides is $21 \mathrm{cm}$. Then, the area of the triangle is: