Answer:
2
Explanation:
If two shapes are similar, this means the ratio of similar sides to each other are the same.
So, in the green shape, the long side length is 5 mm. In the purple shape, the long side length is 10 mm in length. The ratio is therefore 5 to 10, which can be simplified to 1 to 2 (which is basically saying that the side lengths of the purple shape are double the length of the sides of the green shape).
Using the same 1 to 2 ratio, you know that the short side length on the green shape is 1. The short side length on the purple shape (j) must therefore be double, which is 2.