To calculate the focal length of a reading glass (convex lens), we can use the lens formula:

1/f = 1/v - 1/u

Given:

v = -75 cm (distance of distinct vision, negative because it's on the same side as the object)

u = -25 cm (normal near point, assume)

However, since the normal near point is not given, we'll use the formula for a simple magnifier:

f = D / (D/d - 1)

where D = 25 cm (normal near point) and d = 75 cm (distance of distinct vision)

f = 25 / (75/25 - 1)

f = 25 / (3 - 1)

f = 25 / 2

f = 37.5 cm

The focal length of the reading glass is 37.5 cm.