Step-by-step explanation:
We have,
Height of object is 5 cm
Object distance from a convex lens is 18 cm
Focal length of convex lens is 10 cm
i.e. h = 5 cm
u = -18 cm
f = +10 cm
Let v is distance of the image from the lens. Using lens formula :

The magnification of lens is :
, h' is height of the image

h' = -5.00 cm (in three significant figures)