Answer
(a) $6.47cm$
(b) $3.96$
Work Step by Step
(a) We can find the distance between watch and the magnifier as
$d_{\circ}=(\frac{1}{f}-\frac{1}{d_i})^{-1}$
We plug in the known values to obtain:
$d_{\circ}=(\frac{1}{8.65}-\frac{1}{-25.6})^{-1}$
$d_{\circ}=6.47cm$
(b) We can find the angular magnification as
$M=1+\frac{N}{f}$
We plug in the known values to obtain:
$M=1+\frac{25.6}{8.65}$
$M=3.96$
