please answer all of them

$5-)$ What minimum diameter of pipe is necessary to carry $85\mathrm{.}7\frac{L}{s}$ of air with a maximum mean

velocity of $5\mathrm{.}64\frac{m}{s}?$

$6-)$ For steady incompressible flow, are the following values of $u$ and $v$ possible?

$($a$)u=4xy+y^2,v=6xy+3x$

$($b$)u=2x^2+y^2,v=-4xy$

$7-)$ A gas flows through a square conduit. At one point along the conduit, the conduit sides are

$0\mathrm{.}100$ m $,$ the velocity is $7\mathrm{.}55\frac{m}{s},$ and the gas's mass density is $($for its particular pressure and

temperature$)1\mathrm{.}09k\frac{g}{m^3}.$ At a second point, the conduit sides are $0\mathrm{.}250$ m and the velocity is $2\mathrm{.}02$

$\frac{m}{s}.$ Find the mass flow rate of the gas and the gas's mass density at the second point.