Pull an x from the first two terms
x(x^3 + y^3) + (x^3 + y^3) Now x^3 + y^3 is a common factor.
(x^3 + y^3)*(x + 1) That should be far enough. It can be factored further by factoring (x^3 + y^3) but there is no point because you can't do anything after that. But in case you want to know how x^3 + y^3 factors
(x^3 + y^3) = (x + y)(x^2 - xy + y^2)
Which means you could write original polynomial as
(x + y)(x^2 - xy + y^2)(x + 1)
Part B
You factored the x out of xy^3 so that you would have a common factor (x^3 + y^3) to pull out as a common factor for the whole polynomial.