a) $\text{E} \text{трихо} =V \rho_{\text {amb }} g=3000 \mathrm{~m}^{3} \times 1,26 \mathrm{~kg} / \mathrm{m}^{3} \times 10 \mathrm{~m} / \mathrm{s}^{2}=37800 \mathrm{~N}$ b) $n_{\text {quente }} T_{\text {quente }}=n_{\text {amb }} T_{\text {amb }} \rightarrow \rho_{\text {quente }} T_{\text {quente }}=\rho_{\text {amb }} T_{\text {amb }}$ $T_{\text {quente }}=\frac{\rho_{\text {amb }}}{\rho_{\text {quente }}} T_{\text {amb }}=\frac{1,26 \mathrm{~kg} / \mathrm{m}^{3}}{1,05 \mathrm{~kg} / \mathrm{m}^{3}} 300 \mathrm{~K}=360 \mathrm{~K}$