Verified answer

OK, let me get this straight. You have "4" times "x^4" times "y" times "x" times "y^3" times "x^3" times "y^4" times "y" times "x".

So, collect all the "x"s, there are 4 + 1 + 3 + 1, giving you x^9.

(exponent rule: when multiplying, you add the exponents)

Collecting the "y"s, there is/are 1 + 3 + 4 + 1, giving you y^9. hmmm

With the 4 in front, the simplified version is 4x^9y^9.

Hope this helps.