Which graph represents the solution set for the inequality 1/2x ≤ 18?

A rectangle ... Any quadrilaterial with two pairs of parallel sides is a parallelogram. And each side will be the same dimension as its opposite. It must be if there are two pairs of parallel sides. And if one interior angle is right, then all the interior angles are right angles. You may have a square, but it is only a special case of a rectangle, which you must have if your figure is constructed with the given constraints.