B and C are correct.
A circle has 360°. 2/3 of that circle is given by
2/3(360) = 720/3 = 240°.
Stu takes half of this, so his piece will have 240/2 = 120°.
He splits the remainder of it between his 2 sisters; 240-120 = 120° left; 120/2 = 60° for each sister's piece.

There are two changes of sign, so there are 2 or 0 possible positive roots.

There are two changes of sign, so there are 2 or 0 possible negative roots.
There are 4,2 or 0 possible non-real roots.
42.5, just need to multiply