If √28 - 6√3 = √3a + b, (where a, b are rationals), value of (a + b) is?

Given equation is,
√28 - 6√3 = √3a + b
By expanding equation,
√ 1 + 27 - 6√3 = √3a + b
⇒ √(1)² + (3√3)² - 2 x 3√3 = ⇒ √3a + b
⇒ √(1 - 3√3)² = √3a + b
⇒ 1 - 3√3 = √3a + b
On comparing the left and right side equation, we get,
a = -3, b = 1
∴ a + b = -3 + 1 = - 2