From the shape of the quadrilateral, we can assume that it is a parallelogram. In a parallelogram, opposite sides are congruent and thus have the same length.
In this case, we are given that two opposite sides have lengths of and . Therefore, since the quantities must be equal, we can write the following equation to solve for : . Solving for , we get:
(Use the Subtraction Property of Equality to subtract from both sides of the equation, which isolates )
(Use the Division Property of Equality to divide both sides of the equation by to get rid of 's coefficient)
If the two linear equations have the same slope, the equations represent the same line. Since a line intersects with itself everywhere, there will be an infinite number of solutions.