If $$\frac{4}{5}$$ of an estate be worth Rs. 16800, then the value of $$\frac{3}{7}$$ of the estate is = ?

Let the value of the estate be Rs. x
$$\eqalign{ & {\text{Then}}\frac{4}{5}{\text{ of }}x = 16800 \cr & \Leftrightarrow x = \left( {\frac{{16800 \times 5}}{4}} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\, = 21000 \cr & \Leftrightarrow \frac{3}{7}x = \left( {\frac{3}{7} \times 21000} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{ = 9000 }} \cr} $$