Factoring by grouping how do i solve it 8r^3-64^2+r-8

Squaring a number is the same as multiplying the number by itself (64⋅64). In this case, 64 squared is 4096.
8r^3−4096+r−8

Subtract 8 from −4096 to get −4104.
8r^3−4104+r

Factor the polynomial using the rational roots theorem.
(r−8)(8r^2+64r+513)

Ibelieve the answer is c i worked it out three times but if my answer is wrong someone correct me