A square garden has an area of 9 square metres. The perimeter of the garden is $N$ metres. What is the value of $N$ ?

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Since $9=3^{2}$, the area of the garden is $3^{2} \mathrm{~m}^{2}$ or $(3 \mathrm{~m}) \times(3 \mathrm{~m})$.

Therefore, the side-length of the garden is $3 \mathrm{~m}$.

The perimeter is $4 \times 3 \mathrm{~m}=12 \mathrm{~m}$, so $N=12$.