ok, the answer is x^2 - 2x +6. You are being asked what is
(x^3 +x^2 +18) / (x+3)
Solve this by comparing co-efficients .....as below
Let x^3 +x^2 +18 = (x+3)(ax^2 +bx +c)
then a=1,by comparing the co-efficients of x^3
now by comparing co-efficients of x^2, 3a +b =1 so b= -2
and comparing constants, 3c =18 so c=6
which gives
x^3 +x^2 +18 =(x+3)(x^2 -2x +6)