A balloon filled with an air sample occupies \( 3 \, \text{L} \) volume at \( 35^\circ \text{C} \). On lowering the temperature to \( T \), the volume decreases to \( 2.5 \, \text{L} \). The temperature \( T \) is: [Assume \( P \)-constant]
If $ X = A \times B $, $ A = \begin{bmatrix} 1 & 2 \\-1 & 1 \end{bmatrix} $, $ B = \begin{bmatrix} 3 & 6 \\5 & 7 \end{bmatrix} $, find $ x_1 + x_2 $.