6. \( c - \frac{1}{15} = 3 \frac{2}{5} \)

\( c = 3 \frac{2}{5} + \frac{1}{15} = \frac{17}{5} + \frac{1}{15} = \frac{51}{15} + \frac{1}{15} = \frac{52}{15} \)