A part in a machine has length L, a square cross section of side length a, coefficient of thermal conductivity k, and conducts heat from one part to...

A part in a machine has length L, a square cross section of side length a, coefficient of thermal conductivity k, and conducts heat from one part to another as shown in the diagram. If the original part is replaced with a new one with the same length but a circular cross section of diameter a, and conducts heat at the same rate, what is the

new part's coefficient of thermal conductivity?

A. 4k/pi

B. 2k/pi

C. k/pi

D. k

Sorry can't post image