Given, $\mathit{P}=+5\mathit{D}$
We have,

$+5=\frac{1}{\mathit{f}}$
$\mathit{f}=\frac{1}{5}\mathrm{m}$
$=\frac{100}{5}=20\mathrm{cm}$
Focal length, $\mathit{f}=20\mathrm{cm}(\mathit{o}\mathit{r}+20\mathrm{cm}$ ).
Since, focal length of the lens is positive.
Therefore, the nature of lens is convex.
Same size and inverted image is formed when
Magnification, $\mathit{m}=-1$
Also,
$\mathit{m}=\frac{\mathit{v}}{\mathit{u}}$
$\mathit{v}=-\mathit{u}$
From the lens formula,
$\frac{1}{\mathit{v}}-\frac{1}{\mathit{u}}=\frac{1}{\mathit{f}}$
$-\frac{1}{\mathit{u}}+\frac{1}{\mathit{u}}=\frac{1}{\mathit{f}}$
$\frac{-2}{\mathit{u}}=\frac{1}{\mathit{f}}$
$\mathit{u}=-2\mathit{f}$
$\mathit{u}=-2\times 20\left[\because \mathit{f}=20\mathrm{cm}\right]$
$=-40\mathrm{cm}.$