Geometry: Common Core (15th Edition)

$x = 24$
If two lines are cut by a transversal and alternate interior angles are congruent, then those lines are parallel. Let's set the two angles equal to one another: $m \angle BAC = m \angle DCA$ Plug in our knowns from the diagram: $2x + 15 = 4x - 33$ Subtract $15$ from each side of the equation to move constants to the right side of the equation: $2x = 4x - 48$ Subtract $4x$ from each side of the equation to move the variable to the left side of the equation: $-2x = -48$ Divide both sides of the equation by $-2$ to solve for $x$: $x = 24$