Basically you’re multiplying them both
(x^3 + 2x - 1)(x^4 - x^3 + 3)
so you need to make sure you multiply each one, if you do it right, you should end up with
x^7 - x^6 + 3x^3 + 2x^5 - 2x^4 + 6x -x^4 +x^3 -3
simplify by adding like terms
x^7 - x^6 + 2x^5 - 3x^4 + 4x^3 + 6x - 3
your answer would be the third option
Since y is less than x by 7 times
so in terms of x we write
x=7y
