What measure of a will make this quadrillateral a parallelogram?

To determine if a quadrilateral is a parallelogram, you need to show that either pairs of opposite sides are equal in length, or that pairs of opposite angles are equal, or that the diagonals bisect each other. Alternatively, if both pairs of opposite sides are parallel, it also confirms that the quadrilateral is a parallelogram. Any one of these conditions is sufficient to classify the quadrilateral as a parallelogram.