$\begin {array} {1 1}(a)\;T_1 = 1684.0K ; T_2 = 2143.37K\\(b)\;T_1=1234K;T_2 = 1298.3K\\(c)\;T_1=2378.3K;T_2=1369.3K\\(d)\;T_1=3456.1K;T_2=3139.6K \end {array}$