Correct option is (A) 8
The ratio of perimeter of two similar triangles is equal to the ratio of their corresponding sides.
\(\therefore\) \(\frac{\text{Perimeter of first triangle}}{\text{Perimeter of second triangle}}\) \(=\frac{\text{Side of first triangle}}{\text{Corresponding side of second triangle}}\)
\(\Rightarrow\) \(\frac{12}{\text{Corresponding side of second triangle}}=\frac{30}{20}\)
\(\Rightarrow\) Corresponding side of second triangle \(=12\times\frac{20}{30}\)
\(=\frac{24}3=8\,cm\)
