Answer
$8.4cm$
Work Step by Step
We know that
$d_i=(\frac{1}{f}-\frac{1}{d_{\circ}})^{-1}$
We plug in the known values to obtain:
$d_i=(\frac{1}{-0.085}-\frac{1}{8.5})^{-1}$
$d_i=-8.4cm$
Now the far point distance is $|d_i|=8.4cm$
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