Answer
$6(x-4)(x-7)$
Work Step by Step
To factor by trial and error, first check if you can pull out the greatest common factor of the terms. Then determine the two numbers that, when multiplied, equal the third term, and, when added, equal the coefficient of the middle term.
$6x^2-66x+168$
$6(x^2-11x+28)$
$6(x-4)(x-7)$