To solve the expression \(4.31 \times \left(\frac{6}{7} / 8 - \frac{5}{7} / 8\right)\), we first simplify the terms inside the parentheses.
First, simplify \(\frac{6}{7} / 8\) and \(\frac{5}{7} / 8\):
\[ \frac{6}{7} / 8 = \frac{6}{7 \times 8} = \frac{6}{56} = \frac{3}{28} \]
\[ \frac{5}{7} / 8 = \frac{5}{7 \times 8} = \frac{5}{56} \]
Now subtract the two results:
\[ \frac{3}{28} - \frac{5}{56} \]
To subtract these fractions, we need a common denominator. The least common denominator of 28 and 56 is 56.
Convert \(\frac{3}{28}\) to a fraction with a denominator of 56:
\[ \frac{3}{28} = \frac{3 \times 2}{28 \times 2} = \frac{6}{56} \]
Now subtract:
\[ \frac{6}{56} - \frac{5}{56} = \frac{6 - 5}{56} = \frac{1}{56} \]
Now we substitute this back into the original expression:
\[ 4.31 \times \frac{1}{56} \]
Calculate:
\[ 4.31 \div 56 = 0.07625 \]
Thus, the final result is:
\[ \boxed{0.07625} \]