Here, $\mathit{n}=$ the number of months for which the money is deposited = $2\times 12=24$.
$\mathit{r}=6\%,\mathrm{I}=\mathit{₹}1,200$
Let the monthly instalment be $\mathit{₹}\mathit{x}$, then $\mathrm{P}={\mathrm{F}}_{\mathit{x}}$
Using the formula S.I.
$=\mathrm{P}\times \frac{\mathit{n}\left(\mathit{n}+1\right)}{2\times 12}\times \frac{\mathit{r}}{100}$
$1,200=\frac{\mathit{x}\times 24\times 25}{2\times 12}\times \frac{6}{100}$
$\frac{3}{2}\mathit{x}=1,200$
$\Rightarrow \mathit{x}=\mathit{₹}800$
Hence monthly instalment $=\mathit{₹}800$