Cubic systems with seven invariant straight lines of configuration $(3,3,1)$

We classify all cubic differential systems with exactly seven invariant straight lines (taking into account their parallel multiplicity) which form a configuration of type $(3,3,1)$. We prove that there are six different topological classes of such systems. For every class we carried out the qualitative investigation on the Poincaré disc. Some properties of cubic systems with invariant straight lines are given.