$7\mathrm{.}8$ Heating up a strip of natural rubber from $T_1=300K$ to $T_2=350K$ increases the stress at constant elongation $=2$ from ${}_1=4\mathrm{.}3{10}^{5}Pa$ to ${}_2=5{10}^{5}Pa.$ Assuming a linear dependence of stress on temperature at constant elongation, estimate the energetic ${}_E$ and entropic ${}_S$ contributions to the stress at $T_1=300K.$