ANSWERS:

3.(x-3)(x-2)=12
  x²-3x-2x+6=12
  x²-5x-6
  (x-6)(x+1)
  x=6 x=-1

4.x(x+4)=21
  x²+4x=21
  x²+4x-21
  (x+7)(x-3)
  x=-7 x=3

5.x(x-1)=4(3x-10)
  x²-x=12x-40
  x²-13x+40
  (x-8)(x-5)
   x=8 x=5
       
6.x²+2x-3=12
  x²+2x-15
  (x+5)(x-3)
   x=-5 x=3

7.x(x-16)=3(24-5x)
  x²-16x=72-15x
  x²-x-72
  (x-9)(x+8)
   x=9 x=8  

8.(2x-5)(3x+2)=2(3x-11)
   6x²+4x-15x-10=6x-22
   6x²-11x-10-6x+22
   6x²-17x+12
   (3x-4)(2x-3)
        4            3
   x=  ___      x=  ___  
        3            2

9.(2x+1)(x-5)-(x-3)²+(x-2)(x+5)=-23-x
   2x²+x-10x-5-(x²-6x+9)+x²-2x+5x-10=-23-x
   2x²-9x-5-x²+6x-9+x²+3x-10+23+x
   2x²+x-24+23
   2x²+x-1
   (2x-1)(x+1)
        1
   x=  ___     x= -1
        2 

10.4(x-1)(x+1)-4(x-2)=12(x-1)+1
   4(x²-1)-4x+8=12x-12+1
   4x²-4-4x+8-12+12-1
   4x²-16x+5
   (2x-3) (2x-5)
       3          5
   x= ___     x= ___        
       2          2