What Is The Answer ? 3x2 - 15x 18 = 0

Your equation is not complete. It is missing a sign.
If it is
  3x^2 - 15x - 18 = 0
  3(x+1)(x-6) = 0
  x = {-1, +6}

If it is
  3x^2 - 15x + 18 = 0
  3(x-2)(x-3) = 0
  x = {2, 3}