In a double pipe heat exchanger if the inner diameter of inner pipe is $6$cms$,$ and outer diameter is $8$ cms$.$ respectively and pipe has a length of one metre $.$If the rate of heat transferred is $60$ W$.$ overall heat transfer coefficient based on out side diameter is if temperature differene is $60\backslash$deg C Select one:

a$.1\mathrm{.}56$ W$/$m$^2\backslash$deg C

b$.0\mathrm{.}000156$ W$/$m$^2*$C

c$\mathrm{.}0\mathrm{.}00156$ W$/$m$^2*$C

d$.0\mathrm{.}0156$W$/$m$^2*$C