Sequences, Series, and the Binomial Theorem · Medium problem

$16x^4+96x^3+216x^2-216x+81$

$16x^4-96x^3+216x^2-216x+81$

$16x^4-96x^3+216x^2-216x+82$

$16x^{5}-96x^3+216x^2-216x+81$