(b-3)(b-4)-(b+4)в = b^2 - 4b - 3b + 12 - b + 4 = b^2 - 8b + 16

To simplify the expression further, we square the quantity:

(b^2 - 8b + 16)^2 = (b^2 - 8b + 16)(b^2 - 8b + 16)
= b^4 - 8b^3 + 16b^2 - 8b^3 + 64b^2 - 128b + 16b^2 - 128b + 256
= b^4 - 16b^3 + 96b^2 - 256b + 256

Therefore, the simplified expression is b^4 - 16b^3 + 96b^2 - 256b + 256.

For the second expression 20x + 5(x-2), we square the quantity:

(20x + 5(x-2))^2 = (20x + 5x - 10)^2
= (25x - 10)^2
= (25x - 10)(25x - 10)
= 625x^2 - 250x - 250x + 100
= 625x^2 - 500x + 100

Therefore, the simplified expression is 625x^2 - 500x + 100.