a, 27x3 - 27x2 +18x-4=27x3 - 9x2 -18x2 +6x +12x-4
= 9x2(3x-1) - 6x(3x-1) + 4(3x-1)
= (3x-1)(9x2-6x+4)
b, 2x3-x2+5x+3 =\(2x^3+x^2-2x^2-x+6x+3\)
\(=x^2\left(2x+1\right)-x\left(2x+1\right)+3\left(2x+1\right)\)
\(=\left(2x+1\right)\left(x^2-x+3\right)\)