\[\frac{ax - ay + 3x - 3y}{a^{2} - 9} =\]
\[= \frac{a(x - y) + 3 \cdot (x - y)}{a^{2} - 9} = \frac{(x - y)(a + 3)}{(a - 3)(a + 3)} =\]
\[= \frac{x - y}{a - 3}\]
\[При\ x = 5,8;\ \ y = 3,4;\ \ a = 3,1:\]
\[\frac{5,8 - 3,4}{3,1 - 3} = \frac{2,4}{0,1} = \frac{24}{1} = 24.\]