To solve this problem we use an amplification formula for divergent lenses
[tex]M = \frac{i}{o} = \frac{h'}{h}[/tex]
Where:
i: distance of the image to the lens
o: Distance from the object to the lens
h = height of the object
h '= height of the image
[tex]M = \frac{4mm}{12mm} = \frac{h'}{18mm}[/tex]
[tex]h'= 18mm\frac{4mm}{12mm}[/tex]
h '= 6 mm
The height is 6 mm