The formula of force between two current-carrying wire placed parallel to each other in terms of current in each wire and separation between two wires is, 
$F=\frac{{\mu }_0}{2\pi r}\times i_1{i}_2\times l$, the value is given, 
$\frac{F}{l}=4\times {10}^{-5} \mathrm{N} {\mathrm{m}}^{-1}$, 

$$\begin{gathered} \Rightarrow \frac{F}{l}=\frac{{\mu }_0}{2\pi r}\times i_1{i}_2\Rightarrow i_2=\frac{F}{l\times \frac{{\mu }_0}{2\pi r}\times i_1} \\ \Rightarrow i_2=\frac{4\times {10}^{-5}\times 2.50\times {10}^{-2}}{2\times {10}^{-7}\times 0.5}=\frac{2\times 2.50}{0.5}=10 \mathrm{A} \end{gathered}$$