5b²/a²-49b²:b/a²+7ab
5b²/a²-49b²:b/a²+7ab = 5b²/(a-7b)(a+7b) * a(a+7b)/b = 5ab/(a-7b)
5b²/(a-7b)(a+7b) *a(a+7b)/b=5ab/(a-7b)