7ab a - b
-------------- - --------------
a^2 - b^2 a + b
7ab a - b
= -------------- - --------------
(a-b)(a+b) a + b
7ab (a - b)^2
= -------------- - -----------------------
(a-b)(a+b) (a + b)(a-b)
7ab a^2 - 2ab + b^2
= -------------- - -----------------------
(a-b)(a+b) (a + b)(a-b)
7ab - a^2 + 2ab - b^2
= -----------------------------------
(a-b)(a+b)
- a^2 + 9ab - b^2
= -----------------------------------
(a-b)(a+b)
Answer is A. first one
