10+2b/25-b^2 - 2/b-5 + 4/b
10+2b/(5+b)(5-b) - 2/b-5 + 4/b
10+2b/(5+b)(5-b) + 2/5+b + 4/b
[10+2b/(5+b)(5-b)]*b + (2/(5+b))*(b(5-b)) + (4/b)*(5+b)(5-b)
10b+2b^2/b(5+b)(5-b) + 10b-2b^2/b(5+b)(5-b) + 100-4b^2/b(5+b)(5-b)
Опускаем знаменатели
10b + 2b^2 + 10b - 2b^2 + 100 - 4b^2
-4b^2 + 20b + 100 = 0 | : (-1)
4b^2 - 20b - 100 = 0
Ответ : 4b^2 - 20b - 100
Надеюсь, помог.