  The relativistic four-quark equations are found in the framework of
coupled-channel formalism. The dynamical mixing of the meson-meson states with
the four-quark states is considered. The four-quark amplitudes of the
tetraquarks, including $u$, $d$, $s$ and bottom quarks, are constructed. The
poles of these amplitudes determine the masses and widths of $S$-wave bottom
tetraquarks.
