Callum is examining a square stamp of side 3.00 cm with a magnifying glass of refractive power

Question:

Callum is examining a square stamp of side 3.00 cm with a magnifying glass of refractive power + 40.0 D. The magnifier forms an image of the stamp at a distance of 25.0 cm. Assume that Callum's eye is close to the magnifying glass.
(a) What is the distance between the stamp and the magnifier?
(b) What is the angular magnification?
(c) How large is the image formed by the magnifier?