An incompressible liquid flows through a horizontal tube as shown in the figure. Then, the velocity of the fluid is

If the liquid is incompressible, then mass of liquid entering through left end should be equal to mass of liquid coming out from the right end.

$M=M_1+M_2$

$A{V}_1=A{V}_2+1.5A\times v$

$3\mathrm{A}=1.5\mathrm{A}+1.5\mathrm{Av}$

$v=1\mathrm{m}/\mathrm{s}$