A body of length $1 \mathrm{~m}$ having cross-sectional area $0.75 \mathrm{~m}^{2}$ has thermal conductivity $6000 \mathrm{~J} / \mathrm{s}$ then the temperature difference if $\mathrm{K}=200 \mathrm{Jm}^{-1} \mathrm{~K}^{-1}$, will be :
(a) $20^{\circ} \mathrm{C}$
(b) $40^{\circ} \mathrm{C}$
(c) $80^{\circ} \mathrm{C}$
(d) $100^{\circ} \mathrm{C}$