Answer: Side of a square plot = 25 m

Therefore, Area of the house = length x breadth = 20 x 15 = 300 m2
Area of garden = Area of square plot – Area of house = 625 – 300 = 325 m2
Cost of developing the garden per sq. m = ₹ 55
Therefore, Cost of developing the garden 325 sq. m = ₹ 55 x 325 = ₹ 17,875
Hence total cost of developing a garden around is ₹ 17,875.