Help. I don’t know what to do.

(x + 1)^3  =  x^3  + 3x^2  + 3x  + 1

All  we  require is that  some  q(x)  can be  found such that  the x^3  and 3x^2  terms in the first polynomial can be canceled

Let  q (x)   be     (-x - 3)

So notice that

x^2   * q(x)  =   x^2  (-x - 3)   =  -x^3 -3x^2

So

x^3  + 3x^2  + 3x  + 1    +   (-x^3 - 3x^2)  =

3x  + 1

And  this is a polynomial  of  less than degree 2

(Note that  the choice of q(x)  isn't unique.... there are many other possibilities)