Add Like Terms, If Possible, and Write the Result in Descending

Multiple Choice

Add like terms, if possible, and write the result in descending powers of the variable.
-4x^{6 + 8}x² + 9x⁶

A) 13x^{6 + 8}x²
B) 21x¹⁴
C) 21x²
D) Cannot be simplified