An airflow $($density $1\mathrm{.}2$ kg$/$m$^3)$ enters a duct with a cross$-$sectional area of $0\mathrm{.}4$ m$^2$ and a velocity of $3$ m$/$s$.$ The duct splits into two, with one branch having an area of $0\mathrm{.}2$ m$^2$ and a velocity of $4$ m$/$s$.$ What is the velocity in the other branch if its area is $0\mathrm{.}1$ m$^2?$