Answer
$i=5.3cm$
Work Step by Step
Since the lens is converging, the focal length is positive (f=4.0cm). Use the lens equation $$\frac{1}{f}=\frac{1}{i}+\frac{1}{p}$$ to solve for $i$. $$\frac{1}{i}=\frac{p}{pf}-\frac{f}{pf}$$ $$\frac{1}{i}=\frac{p-f}{pf}$$ $$i=\frac{pf}{p-f}$$ Substituting values of $f=4.0cm$ and $p=16cm$ yields an image distance of $$i=\frac{(16cm)(4.0cm)}{16cm-4.0cm}=5.3cm$$
