Answer:
x+2
Explanation:
Dividing the poly by the known factor:
x3+5x2+6x | x2+3x
-x3-3x2 x + 2 <- the answer is here
2x2+6x
-2x2-6x
To prove that, let's multiply the two factors and find the pylonomial back on:
(x2+3x).(x+2) = x3 + 2x2 + 3x2 + 6x = x3 + 5x2 + 6x
Tks your attention!