Explanation: 1- solving for r: We are given that: AD is congruent to AB This means that: AD = AB 2r + 8 = 5r - 13 5r - 2r = 8 + 13 3r = 21 r = 21/3 r = 7 2- getting the value of AB: Since we calculated the value of r, we can simply substitute in the equation to get AB as follows: AB = AD = 5(7)-13 = 2(7)+8 = 22 units