7x² - 36x + 12
Since the last term is positive, the signs must be both positive or both negative.
Since the middle term is negative, the signs must be both negative.
There is only one set of factors for 7: 1 and 7.
However, there are many factors for 12: 12 and 1, 6 and 2, 4 and 3 (and they have to be checked both ways).
So the possibilities are:
(7x - 12)(x - 1) (7x - 1)(x - 12) (7x - 6)(x - 2) (7x - 2)(x - 6)
(7x - 4)(x - 3) (7x - 3)(x - 4)
Check each of the above to find the proper factors.
If none of them work, then the problem cannot be factored using whole numbers.