In magnitude form,
\(\begin{aligned} \left|\operatorname{Emf}_{\text {ind }}\right|=\left|(-) \mathrm{L} \frac{\mathrm{di}}{\mathrm{dt}}\right| \\ \Rightarrow 0.1=\frac{(\mathrm{L})[+2-(-2)]}{0.2}\end{aligned}\)
\(\Rightarrow \mathrm{L}=\frac{0.1 \times 0.2}{4}=5 \mathrm{mH}\)