1) 81 - (b+4)^2 = (9 - (b+4))(9 + (b+4)) = (9 - b - 4)(9 + b + 4) = (5 - b)(13 + b)
2) (5n+5)^2 - 16 = ((5n+5) - 4)((5n+5) + 4) = (5n + 1)(5n + 9)
1) 81 - (b+4)^2 = (9 - (b+4))(9 + (b+4)) = (9 - b - 4)(9 + b + 4) = (5 - b)(13 + b)
2) (5n+5)^2 - 16 = ((5n+5) - 4)((5n+5) + 4) = (5n + 1)(5n + 9)