12. Two streets form an intersection. \( \angle C \) and \( \angle D \) are supplementary angles. If the measure of \( \angle C \) is \( 128^{\circ} \) and the measure of \( \angle D \) is two times the value of \( x \), what is the value of \( x \) ?

To solve for \( x \), we use the information that angles \( \angle C \) and \( \angle D \) are supplementary. This means their measures add up to \( 180^{\circ} \). Given: - \( \angle C = 128^{\circ} \) - \( \angle D = 2x \) We can set up the equation: \[ \angle C + \angle D = 180^{\circ} \] Substituting the known values, we have: \[ 128^{\circ} + 2x = 180^{\circ} \] Now, subtract \( 128^{\circ} \) from both sides: \[ 2x = 180^{\circ} - 128^{\circ} \] \[ 2x = 52^{\circ} \] Now, divide both sides by 2 to solve for \( x \): \[ x = \frac{52^{\circ}}{2} = 26^{\circ} \] Thus, the value of \( x \) is \( 26^{\circ} \).