Considering first statement only, nothing absolute can be said about the value of $$a^3 + b^3$$ similarly considering 2nd statement only nothing absolute can be said about the value of $$a^3 + b^3$$.
When we consider both statements together two values of (a+b) can be possible as $$\sqrt{28}$$ and $$-\sqrt{28}$$
By which two possible values of $$a^3 + b^3$$. Nothing absolute can be said about it.
Hence answer will be D).