Hello!
I believe the answer is (3x^2 - 3x + 5) • (x + 1)
I hope it helps!
set up synthdiv for (3x^4+6x^3+2x^2+9x+10)/ (x+2)
test zero at x=-2
-2 | 3 6 2 9 10
........ -6 0 -4 -10
---------------------------------
..... 3 0 2 5 0
so the ans is 3x^3+2x+5
