Vertical angles are pairs of opposite angles formed by two intersecting lines, and they are always equal in measure. If the sum of the measures of two vertical angles is 300°, then we can set up the following equation:
Let \( x \) be the measure of each vertical angle.
Since the angles are equal: \[ x + x = 300° \] \[ 2x = 300° \] \[ x = \frac{300°}{2} = 150° \]
Therefore, each angle measures \( 150° \). The correct response is: 150°.