Final answer:
If a quadrilateral has both pairs of opposite sides parallel, it is a parallelogram.
Step-by-step explanation:
To determine whether a figure is a parallelogram, we can use the concept of slopes. If two pairs of opposite sides of a quadrilateral are parallel, then it is a parallelogram. In this case, if lines a and b are parallel, and lines c and d are parallel, it implies that the figure is a parallelogram.
The value of x does not need to be determined for this question, as the given information already confirms that the figure is a parallelogram with both pairs of opposite sides parallel.