Geometry: Common Core (15th Edition)

$x = 4$
In similar figures, corresponding sides are proportional. Each set of corresponding sides has the same ratio. Let's set up a proportion to set the ratios of sides equal to one another: $\frac{2}{x} = \frac{4}{8}$ Use the cross products property to eliminate the fractions: $4x = 16$ Divide each side of the equation by $4$ to solve for $x$: $x = 4$