6х(х-3)-х(2-х) = 6х(х-3)+х(x-2) = 6x^2 - 18x + x^2 - 2x = 7x^2 - 20x= x(7x-20)
2х(21)(4+х) = 42x*(4+x)= 168x + 42x^2 = 42x^2 + 168x = 42x(x+4)
