Your factors must begin 3x and x to give 3x2. The factors of 12 are 1/12, 2/6 and 3/4. Which pair, together with 3x and x, can add to -5? 3 and 4 seem to fit the bill:
(3x + 4)(x - 3)
3x(6x - 1)
It is: (3x+4)(2x-3) when factored
(x + 3)(3x - 2)
3x2-x-2 = (3x+2)(x-1)
It is: (2x+3)(3x-8) when factored
3x squared minus 25x minus 28
x(3x - 2)
3x(6x - 1)
(x-3)(3x+1)
(3x + 8)(3x - 8)
(3x + 1)(x - 5)
It is: (3x+4)(2x-3) when factored
(x + 3)(3x - 2)
3x2-x-2 = (3x+2)(x-1)
(x + 2)(3x - 1)(3x + 1)
It is: (2x+3)(3x-8) when factored
3x^2 -14x +15 = (3x-5)(x-3)