Problem $4($L$03)/(15$ points$)$:

A certain part of cast iron piping of a water distribution system involves a parallel section. Both parallel pipes have a diameter of $30cm,$ and the flow is fully turbulent. One of the branches $($pipe $A)$ is $1000m$ long while the other branch $($pipe $B)$ is $3000m$ long. If the flow rate through pipe $A$ is $0\mathrm{.}4m\frac{3}{s},$ determine the flow rate through pipe B$.$ Disregard minor losses. $)=999\mathrm{.}1\frac{kg}{m^2},=(1\mathrm{.}138{10}^{-2}\frac{kg}{m}.s$