The factors of 180 are
(1, 180), (2, 90), (3, 60), (4, 45), (5, 36), (6, 30), (9, 20), (10, 18), (12, 15).
The GCD of 6 is the largest positive integer that divides 180.
Therefore the required factors of 180 are a=6 and b=30 or vice versa.
a + b = 6 +30 = 36
Answer: 36