Verified Answer :

(6y - 11)(6y + 11) = ay² - b    |use (a - b)(a + b) = a² - b²

(6y)² - 11² =ay² - b

36y² - 121 = ay² - b    |add b to both sides

ay² = 36y² - 121 + b        |divide both sides by y² ≠ 0

a = (36y² - 121 + b)/y²

\(\boxed{a=\dfrac{36y^2-121+b}{y^2}}\)