We can find the value of y in the expression y² + 7y + 12 by factorising.
Make the expression equal to zero.
y² + 7y + 12 = 0
Factorise.
(y + 3)(y + 4) = 0
So either (y + 3) = 0 or (y + 4) = 0
When (y + 3) = 0, y would be -3.
When (y + 4) = 0, y would be -4.