Find the indefinite integral using the power rule: ∫ x(x+9)^(5) dx. Which of the following options correctly represents the antiderivative of the given expression?
A. ∫ (x^7 + 9x^6) dx
B. ∫ (x^6 + 9x^5) dx
C. ∫ (x^6 + 9x^4) dx
D. ∫ (x^7 + 9x^5) dx