Priya wears +1.5 D glasses to achieve normal vision from 25 cm...

The power of the simple microscope lens is given as $P = 20 \text{ D}$.

The focal length of the microscope lens is:
$f = \dfrac{100}{P} = \dfrac{100}{20} = 5 \text{ cm}$

Priya wears glasses to achieve normal vision from $25 \text{ cm}$ onwards. When she uses the microscope together with her glasses, her eye effectively behaves as a normal eye with a near point (least distance of distinct vision)$of D = 25 \text{ cm}$.

The maximum magnifying power of a simple microscope is achieved when the final image is formed at the near point. The formula for maximum magnifying power is:
$M = 1 + \dfrac{D}{f}$

Substituting the values of $D$ and $f$:
$M = 1 + \dfrac{25}{5}$

$M = 1 + 5 = 6$