A rectangular slab of material with cross$-$section area A and length $d$ with one side held at temperature $T_1$ and the other side held at temperature $T_2$ is observed to have a rate of heat transfer of $10\frac{J}{s}.$ Another slab of the same material has cross$-$section area $2$ A and length $6$ d $.$ It will have a rate of heat transfer of

$60\mathrm{.}0\frac{J}{s}$

$1\mathrm{.}67\frac{J}{s}$

$3\mathrm{.}33\frac{J}{s}$

$30\mathrm{.}0\frac{J}{s}$