Formula: 1 Mark
Steps: 2 Marks
Answer: 1 Mark
Given that 
The cost of painting is Rs10 per $c{m}^2$.
The length of the rectangular wall=400 cm
The breadth of the rectangular wall=900 cm
Area of the rectangle =  length $\times$ breadth
On substituting the values we get

Area of the rectangle = (400) $\times$ (900)

  = 360000 $c{m}^2$

Money required to paint the rectangular wall = (10) $\times$ (360000)

= Rs.3600000
The diameter of the circular wall = 126 cm.
Radius of the wall, $r$ = $1262$ = 63 cm
The area a circle is given by, Area = $\pi \times r^2$
On substituting the values we get,
Area of the circular wall
= $\frac{22}{7}\times 63\times 63$ = 12474 $c{m}^2$
Money required to paint the circular wall
 = 12474$\times$10 = Rs 124740
The total cost of painting
= 3600000 + 124740 = Rs 3724740
Hence, the total cost of painting the walls is Rs 37,24,740.