The fractions $\displaystyle\frac{6}{7}$ and $\displaystyle \frac{{13}}{5}$ have diffrent denominators, so we find the LCD to turn them into equivalent one´s.

LCD(7, 5) = 35

$ \displaystyle \frac{6}{7}\times \frac{5}{5}=\frac{{30}}{{35}}$

$\displaystyle \frac{{13}}{5}\times \frac{7}{7}=\frac{{91}}{{35}}$

Add the numerators and leave the denominator as it is :$\displaystyle

\frac{{30}}{{35}}+\frac{{91}}{{35}}=\frac{{121}}{{35}}$

So, $\displaystyle \frac{6}{7}+2\frac{3}{5}=\frac{{121}}{{35}}$