Height of Towers

Let $x$ be the estimated height in $\text{mm}$ . By direct counting, the number of pens is $22$ . Then by ratio and proportion,

$\dfrac{x}{100}=\dfrac{88}{22}$

$x=\dfrac{88\times 100}{22} = \boxed{400 ~\text{mm}}$

A pair of pens make a layer of tower. There are 11 layers of tower or 11 pairs of pens in the picture. Therefore each pair of pens is $\dfrac {88}{11} = 8 \text{ mm}$ high. And 100 or 50 pairs of pens has a height of $50 \times 8 = \boxed{400 \text{ mm}}$ .