If CAT and BOAT are written as XZG and YLZG respectively in a code language, how is EGG to be written?

The pattern maps each letter to its reverse alphabetic position ($1\leftrightarrow 26$, $2\leftrightarrow 25$, etc.):
* $\text{C}\leftrightarrow \text{X}$, $\text{A}\leftrightarrow \text{Z}$, $\text{T}\leftrightarrow \text{G}$
* $\text{B}\leftrightarrow \text{Y}$, $\text{O}\leftrightarrow \text{L}$, $\text{A}\leftrightarrow \text{Z}$, $\text{T}\leftrightarrow \text{G}$

Applying the same reverse mapping to $\text{EGG}$:

* $\text{E}$ (5th from start) $\leftrightarrow \text{V}$ (5th from end)
* $\text{G}$ (7th from start) $\leftrightarrow \text{T}$ (7th from end)
* $\text{G}$ (7th from start) $\leftrightarrow \text{T}$ (7th from end)

Thus, $\text{EGG}$ is coded as $\text{VTT}$.