Question

how to find the length if perimeter and breadth are given?

Answer 1

If your question if for rectangle, then the solution is as follows:
$$\begin{gathered} \mathrm{We}\mathrm{know}\mathrm{that}, \\ \mathrm{Perimeter}\mathrm{of}\mathrm{rectangle}=2\left(\mathrm{Length}+\mathrm{Breadth}\right) \\ \Rightarrow \frac{\mathrm{Perimeter}\mathrm{of}\mathrm{rectangle}}{2}=\mathrm{Length}+\mathrm{Breadth} \\ \Rightarrow \mathbf{Breadth}\mathbf{=}\frac{\mathbf{Perimeter}\mathbf{}\mathbf{of}\mathbf{}\mathbf{rectangle}}{\mathbf{2}}\mathbf{-}\mathbf{Length} \end{gathered}$$