Let's solve each of the given expressions step by step.

### a. \(-\frac{9}{7} \times \left( \frac{14}{15} - -\frac{7}{9} \right)\)

First, simplify inside the parentheses:
\[
\frac{14}{15} - -\frac{7}{9} = \frac{14}{15} + \frac{7}{9}
\]

To add these fractions, find a common denominator. The least common multiple of 15 and 9 is 45.

Convert each fraction:
\[
\frac{14}{15} = \frac{14 \times 3}{15 \times 3} = \frac{42}{45}
\]
\[
\frac{7}{9} = \frac{7 \times 5}{9 \times 5} = \frac{35}{45}
\]

Now add the fractions:
\[
\frac{42}{45} + \frac{35}{45} = \frac{42 + 35}{45} = \frac{77}{45}
\]

Now multiply by \(-\frac{9}{7}\):
\[
-\frac{9}{7} \times \frac{77}{45}
\]

Simplify the multiplication:
\[
-\frac{9 \times 77}{7 \times 45} = -\frac{693}{315}
\]

Simplify the fraction:
\[
-\frac{693}{315} = -\frac{231}{105} = -\frac{77}{35} = -\frac{11}{5}
\]

So, the result for part (a) is:
\[
-\frac{11}{5}
\]

### b. \(-\frac{5}{7} \times \left( \frac{2}{-3} + -\frac{7}{8} \right)\)

First, simplify inside the parentheses:
\[
\frac{2}{-3} + -\frac{7}{8} = -\frac{2}{3} - \frac{7}{8}
\]

To add these fractions, find a common denominator. The least common multiple of 3 and 8 is 24.

Convert each fraction:
\[
-\frac{2}{3} = -\frac{2 \times 8}{3 \times 8} = -\frac{16}{24}
\]
\[
-\frac{7}{8} = -\frac{7 \times 3}{8 \times 3} = -\frac{21}{24}
\]

Now add the fractions:
\[
-\frac{16}{24} - \frac{21}{24} = -\frac{16 + 21}{24} = -\frac{37}{24}
\]

Now multiply by \(-\frac{5}{7}\):
\[
-\frac{5}{7} \times -\frac{37}{24}
\]

Simplify the multiplication:
\[
\frac{5 \times 37}{7 \times 24} = \frac{185}{168}
\]

So, the result for part (b) is:
\[
\frac{185}{168} = \frac{185}{168}
\]

### c. \(\left( \frac{23}{41} - \frac{15}{82} \right) \times \frac{41}{25}\)

First, simplify inside the parentheses:
\[
\frac{23}{41} - \frac{15}{82}
\]

To subtract these fractions, find a common denominator. The least common multiple of 41 and 82 is 82.

Convert each fraction:
\[
\frac{23}{41} = \frac{23 \times 2}{41 \times 2} = \frac{46}{82}
\]

Now subtract the fractions:
\[
\frac{46}{82} - \frac{15}{82} = \frac{46 - 15}{82} = \frac{31}{82}
\]

Now multiply by \(\frac{41}{25}\):
\[
\frac{31}{82} \times \frac{41}{25}
\]

Simplify the multiplication:
\[
\frac{31 \times 41}{82 \times 25} = \frac{1271}{2050}
\]

So, the result for part (c) is:
\[
\frac{1271}{2050}
\]

### Summary:
a. \(-\frac{11}{5}\)
b. \(\frac{185}{168}\)
c. \(\frac{1271}{2050}\)