A fluid with viscosity $0\mathrm{.}01$ Pa$.$s and density $1800$ kg$/$m$3$

is flowing through a pipe with radius $12$ cm at a flow

rate of $0\mathrm{.}01$ m$3/$s$.$ Calculate the friction factor if the wall roughness is $($a$)=0,($b$)=100$m$,($c$)=2$ mm$.$