Isosceles trapezoid W X Y Z is shown. Sides X Y and W Z are parallel. The length of X Y is 3 a minus 4 and the length of W Z is 3 a. Sides W X and Y Z are congruent. The length of W X is 2 a minus 2 and the length of Y Z is a + 1.
What is the length of XY?
3 units
4 units
5 units
6 units