Elementary Geometry for College Students (7th Edition)

$x^2 + 7x + 12$
By using the FOIL method, we multiply the first, outside, inside, and the last element of each bracket and we add them. $(x+3)(x+4) = x\times x + x\times 4 + 3\times x + 3\times 4 = x^2 + 7x + 12$