x2 - 7x - 8 =0
To solve for this you want two factors of 8 that when added together is -7 and when multiplied is -8.
Given the multiple choice we know the correct factors are 1 and 8. We also know that one of the terms must be negative, that way you'll have to numbers that multiply to -8.
So it's either -1 and 8 or 1 and -8. Since 1 + -8 = -7, We know that the correct choice is 1, -8 or B.