y^2 + 15y + 56 factors to (y+7)(y+8)
This is because 7+8 = 15 is the middle term and 7*8 = 56 is the last term. We can use the box method, FOIL rule, or distributive property to confirm we have the right factorization. I'll use the distributive rule
(y+7)(y+8) = y(y+8) + 7(y+8)
(y+7)(y+8) = y^2 + 8y + 7y + 56
(y+7)(y+8) = y^2 + 15y + 56
