Find the range of values of m for which the function 3x^2 -12x + m is negative for all values of x.

Is it possible for the function to be negative ? If so, how ?I tried using b^2 - 4ac < 0 and the result is m > 12 . However when i tried substituting *13* as the value of m and *1* as the value of x, the result is a positive number.