  The yields of evaporation residues, fusion-fission and quasifission fragments
in the $^{48}$Ca+$^{144,154}$Sm and $^{16}$O+$^{186}$W reactions are analyzed
in the framework of the combined theoretical method based on the dinuclear
system concept and advanced statistical model. The measured yields of
evaporation residues for the $^{48}$Ca+$^{154}$Sm reaction can be well
reproduced. The measured yields of fission fragments are decomposed into
contributions coming from fusion-fission, quasifission, and fast-fission. The
decrease in the measured yield of quasifission fragments in
$^{48}$Ca+$^{154}$Sm at the large collision energies and the lack of
quasifission fragments in the $^{48}$Ca+$^{144}$Sm reaction are explained by
the overlap in mass-angle distributions of the quasifission and fusion-fission
fragments. The investigation of the optimal conditions for the synthesis of the
new element $Z$=120 ($A$=302) show that the $^{54}$Cr+$^{248}$Cm reaction is
preferable in comparison with the $^{58}$Fe+$^{244}$Pu and $^{64}$Ni+$^{238}$U
reactions because the excitation function of the evaporation residues of the
former reaction is some orders of magnitude larger than that for the last two
reactions.
