If the image of an object placed 15 cm from the lens is 30 cm from it, then an increase in the collecting lens.

To calculate the magnification of a thin lens, you only need to know the distance from the object to the lens d and the distance from the lens to the image f. The increase in G is determined by the formula: G = – (f / d). Since the object (source) and images are real (not constructed from the points of intersection of the rays), then the values d = 0.15 m, f = 0.3 m are positive.
G = – (0.30 m / 0.15 m) = – 2.
A minus sign indicates that the image is upside down.
Answer: G = -2.