## Geometry: Common Core (15th Edition)

$y = 2$
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 $y$: $y = 2$