#### Answer

$y = 2$

#### Work Step by Step

A proportion takes the following form:
$\frac{a}{b} = \frac{c}{d}$, where $a$ and $d$ are the extremes and $b$ and $c$ are the means.
In this exercise, $a = y$, $b = 6$, $c = 18$, and $d = 54$.
The extremes are $y$ and $54$. The means are $6$ and $18$.
Let's solve for $y$:
$\frac{y}{6} = \frac{18}{54}$
Use the cross products property to get rid of the fractions:
$54y = 108$
Divide each side by $54$ to solve for $y$:
$y = 2$