To expand on this: the group velocity of holes may be both positive and negative, and it depends on which hole we’re looking at. In the exercise we’re looking at a hole with k>0 and in the valence band. This may mean two things: a hole that is created after removing an electron with k>0. This hole has k<0. Alternatively, the question may refer to a hole that has k>0. The question was ambiguously formulated and referred to the first case.
The dispersion relation of holes in the valence band is
E_h = -E_v + \hbar^2 k^2/2m_h,
which means that the group velocity is v_g = \hbar k / m_h, so it is negative in the second case and positive in the first case.
I have clarified the exercise to refer to the second case (hole with k>0).