What is the remainder obtained by dividing x7 x5 1 by the generator polynomial x3 1?

Please, use " ^ " to indicate exponention.  x7 and  x3 are meaningless.

I must assume you mean x^7 + 0 x^6 + 0x^5 + 0x^4 + 0x^3 + 0x^2 + 0x + 1
and that your "generator polynomial" is   x^3 + 0x^2 + 0x + 1.  If this is not the case, then you really need to work on your presentation of polynomials.

Divide (x^3 + 0x^2 + 0x + 1 into 
     x^7 + 0 x^6 + 0x^5 + 0x^4 + 0x^3 + 0x^2 + 0x + 1

Dividing x^3 into x^7 leaves a partial quotient of x^4.  Multiply (x^3 + 1) by this x^4 and write your result under x^7 + 0x^6 + 0x^5  ...  + 1
Subtract.

Can you now finish this problem?  If not, what do you need to know so that you can finish it?