Помогите, пожалуйста!

121.
1) (b+6)(b-6)-3b(b+2) = b-36-3b-6b = -2b-36-6b = -2b-6b-36
2) (3a-2)(3a+2)+(a-8)(a+8) = 9a-4+a-64 = 10a-68
3) (5x-3y)(5x+3y)+(3x-5y)(3x+5y) = 25x-9y+9x-25y = 34x-34y
4) (c-2)(3-c)-(5-c)(5+c) = 3c-c+6+2c-(25-c) = 3c-c-6+2c-25+c = 5c-31
5) (x-5)-x(x+3) = x-10x+25-x-3x = -13x+25
6) (6a-b)-(9a-b)(4a+2b) = 36a-12ab+b-(36a+18ab-4ab-2b) = 36a-12ab+b-(36a+14ab-2b) = 36a-12ab+b-36a-14ab+2b = -26ab+3b
7) 3x(5+x)-x(3x-6) = 3x(25+10x+x)-x(9x-36x+36) = 75x+30x+3x-9x+36x-36x = 39x+66x-6x = -6x+66x+39x
8) (x-2)+(x-1)(x+1) = x-4x+4+x-1 = 2x-4x+3
9) (3a-2b)(3a+2b)-(a+3b) = 9a-4b-(a+6ab+9b) = 9a-4b-a-6ab-9b = 8a-13b-6ab

123.
1) x-25 = (x-5)(x+5)
2) 36-16y = 4(3-2y)(3+2y)
3) 4x-81y = (2x-9y)(2x+9y)
4) 0,09t-121p = (0,3t-11p)(0,3t+11p)
5) 100a-180ab+81b = (10a-9b)
6) 16m+49n-56mn = 16m-56mn+49n = (4m-7n)

129.
(x-3)-(x+1) = 12
x-6x+9-(x+2x+1) = 12
x-6x+9-x-2x-1 = 12
-8x+8 = 12
-8x = 12-8
-8x = 4
x = - 4/8
x = - 1/2
Ответ: - 1/2

135.
(x+7)+2(x+7)(x-5)+(x-5) = x+14x+49+(2x+14)(x-5)+x-10x+25 = x+14x+49+2x-10x+14x-70+x-10x+25 = 4x+8x+4
4x+8x+4 = 43+83+4 = 49+24+4 = 36+24+4 = 64