$6)$ A solid cylindrical bar conducts heat at a rate of $25$ W from a hot to a cold reservoir under steady

state conditions. If both the length and the diameter of this bar are doubled, the rate at which it will conduct heat between these reservoirs will be

A$)25$ W

B$)50$ W

C$)100$ W

D$)200$ W

E$)12\mathrm{.}5$ W