How do I solve this?

Consider a cylindrical bar of radius $r_0$ and a tube of inner radius $r_1,$ sharing their axis, with a cross

section as shown here:

Calculate the velocity profile for the flow through the ring in the direction $z$ parallel to the axis $($i$.$e$.,$

perpendicular to the page$)$ when a pressure gradient $\frac{p}{L}(L$ is the length of the rod$)$ is applied. Ignore

the effects of gravity. The flow is steady, incompressible and axisymmetric.