An object 4 cm tall is placed 15 cm from a convex lens of focal length 10 cm. The image height is

$\frac1v-\frac1u=\frac1f$, $u=-15$: $\frac1v=\frac1{10}-\frac1{15}=\frac{1}{30}\Rightarrow v=30$. $m=v/u=30/(-15)=-2$. Image height $=|m|\times4=8$ cm, inverted.