The following squares represent the monthly income of two families

If the monthly income of family A is Rs. 40000, the monthly income of family B is ?

$$\frac{{{\text{Monthly income of family A}}}}{{{\text{Monthly income of family B}}}}$$       $$ = \frac{{{\text{Area of square A}}}}{{{\text{Area of square B}}}}$$
$$\eqalign{ & \Rightarrow \frac{{40000}}{x} = \frac{{{2^2}}}{{{3^2}}} \cr & \Rightarrow x = \left( {\frac{{40000 \times 9}}{4}} \right) \cr & \Rightarrow x = 90000 \cr} $$