Hello from MrBillDoesMath!
Answer:
0.5 x^4 + 12.5
Discussion:
Only the constant terms are "like" and can be combined. Nothing combines with x^4.
0.5 ( x^4 - 9) + 17 =
0.5 x^4 - 0.5 (9) + 17 = as 0.5(9) = 4.5
0.5x^4 - 4.5 + 17 =
0.5 x^4 + 12.5
Thank you,
MrB