Answer:
Original length of square flower garden is 12 m.
Step-by-step explanation:
It is given that when the side of the square is increased by 3 m the area will be 225 sq m.
Let initially the length of the square be x. We know that the area of the square is side × side.
So,

On solving the quadratic equation :

x = 12 m
So, the original length of the garden is 12 m.
Hence, the correct option is (c) " 12 cm ".