$\begin{aligned} & \phi=\mathrm{B} \cdot \pi \mathrm{r}^2 \\ & \varepsilon=\frac{\mathrm{d} \phi}{\mathrm{dt}}=\pi \mathrm{r}^2 \frac{\mathrm{~dB}}{\mathrm{dt}} \\ & \mathrm{i}=\frac{\varepsilon}{\mathrm{R}}=\frac{\pi \mathrm{r}^2}{\mathrm{R}} \cdot\left(\frac{\mathrm{dB}}{\mathrm{dt}}\right)=\frac{\pi}{2}\left(\frac{1}{5}\right)^2(4 \mathrm{t}+2) \\ & \text { for } \mathrm{t}=3 \\ & i=\frac{11}{7} \times \frac{1}{25} \times 14 \\ & i=\frac{44}{50}\end{aligned}$