a: \(=6x^3-2x^2-15x^2+5x+9x-3\)
\(=\left(3x-1\right)\left(2x^2-5x+3\right)\)
\(=\left(3x-1\right)\left(x-1\right)\left(2x-3\right)\)
c: \(=x^3-25x+6x-30\)
\(=x\left(x-5\right)\left(x+5\right)+6\left(x-5\right)\)
\(=\left(x-5\right)\left(x^2+5x+6\right)=\left(x-5\right)\left(x+2\right)\left(x+3\right)\)