We have 1 ha = 10000 square metres
So, 0.5 ha = 0.5 * 10000 sq.metres = 5000 sq.metres
Area of rectangle = Length * Breadth = L×B
let L = 12.5 m (given)
Therefore, 5000 sq.m = 12.5×B
B=(5000)(12.5)
B = 400 metres
Hence, the other side length is 400 metres.