Answer: The length of AD is 22 units.
Step-by-step explanation: Given that the quadrilateral ABCD in the figure is a kite. Also, AD is congruent to AB.
We are to find the length of AD.
Also, given in the figure that
AD = 2r + 8 and AB = 5r - 13.
A KITE is a quadrilateral having congruent adjacent sides and the diagonals bisect each other perpendicularly.
Since ABCD is a kite and side AD is adjacent to side AB.
Therefore, we must have

So, the length of AD is given by

Thus, the length of AD is 22 units.