  We compute the flat coordinates on the Frobenius manifolds arising on the
deformation space of Gepner $\hat{SU}(3)_k$ chiral rings. The explicit form of
the flat coordinates is important for exact solutions of models of topological
CFT and 2d Liouville gravity. We describe the case k=3, which is of particular
interest because apart from the relevant chiral fields it contains a marginal
one. Whereas marginal perturbations are relevant in different contexts, their
analysis requires additional care compared to the relevant perturbations.
