A launch plies between two points $A$ and $B$ on the opposite banks of a river always following the line $AB$. The distance $S$ between points $A$ and $B$ is $1200 \mathrm{m}$. The velocity of the river current $u=1.9 \mathrm{m}/\mathrm{s}$ is constant over the entire width of the river. The line $AB$ makes an angle $\alpha =60°$ with the direction of the current. With what velocity $u$ and at what angle $\beta$ to the line $AB$ should the launch move to cover the distance $AB$ and back in a time $t=5 min$? The angle $\beta$ remains the same during the passage from $A$ to $B$ and from $B$ to $A$.