## Algebra 1: Common Core (15th Edition)

$x = 6$
To solve a proportion, we use the cross products property, multiplying the numerator of one ratio with the denominator of the other ratio, and vice versa: $2(21 - x) = 5x$ Distribute on the left side of the equation: $42 - 2x = 5x$ Add $2x$ to both sides of the equation to collect variable terms on the right side of the equation: $42 = 7x$ Divide each side of the equation by $7$ to solve for $x$: $x = 6$