First step to factor the trinomial, multiply the constant -28 with the leading coefficient 6.
So, -28 * 6 = - 168.
Next step is to breakdown -168 into two multiples so that their addition will result the coefficient of w= - 13.
So, -168 = -21 * 8.
And addition of - 21 and 8 will give - 13.
So, next step is to replace -13x with -21x + 8. Therefore,
6x² - 21x + 8x - 28 =0
(6x² - 21x) + (8x - 28 )=0 Make the group of two terms.
3x (2x - 7) + 4 (2x - 7) = 0 Take out the common factor from each group.
(2x - 7)(3x + 4) = 0 Again take out the common factor (2x -7).
So, 2x - 7 =0, 3x + 4 = 0 Set both the factor equal to 0.
2x = 7 , 3x = -4
So,

Hope this helps you !