\textbf{172.} A concave mirror has an object placed on its principal axis, and the image length is $\dfrac{1}{4}$ of the object length. If we move the object to the location of the image, how many times the object length will the new image length be?
\[
(1)\ 16 \qquad (2)\ 8 \qquad (3)\ 4 \qquad (4)\ 1
\]
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\textbf{Workspace for Calculations}
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