If a :b=√7 : √3, then the value of (3a+2b) :(3a-2b) is equal to:

​$$a : b = \sqrt{7} : \sqrt{3} \\$$​​

​$$(a + b)^2 = a^2 + b^2 + 2ab \\(a^2 - b^2) = (a + b)(a - b) \\$$​​

Thus, correct option is (b).