Answer
8.4mm
Work Step by Step
A meter stick at a distance of $2000 \mathrm{~m}$ subtends an angle of
$
\theta_{\text {stick }} \approx \frac{1 \mathrm{~m}}{2000 \mathrm{~m}}=0.0005 \mathrm{rad} \text {. }
$
multiplying this by the mirror focal length gives $(16.8 \mathrm{~m})(0.0005)=8.4 \mathrm{~mm}$ for the size of the image.
