Answer:
Q=260.96W/m
Step-by-step explanation:
you should raise the heat transfer equation between the inner part of the tube and the outer part taking into account the convection and conduction resistances
as they are asking us for the heat per unit length, then the conduction and convection resistances are like this
Rh=1/(hDpi)
Rc=ln(De/Di)/2piK
I attached the complete procedure