$\text{a) $\dfrac{38}{11}+(\dfrac{16}{13}+\dfrac{6}{11})$}$
$\text{= $\dfrac{16}{13}+(\dfrac{38}{11}+\dfrac{6}{11})$}$
$\text{= $\dfrac{16}{13}+\dfrac{44}{11}$}$
$\text{= $\dfrac{16}{13}$ + 4}$
$\text{= $\dfrac{16}{13}+\dfrac{52}{13}$}$
$\text{= $\dfrac{68}{13}$}$
$\text{= $5\dfrac{3}{13}$}$
$\text{b) $\dfrac{3}{4}÷\dfrac{3}{5}-\dfrac{1}{5}$}$
$\text{= $\dfrac{3}{4}×\dfrac{5}{3}-\dfrac{1}{5}$}$
$\text{= $\dfrac{5}{4}-\dfrac{1}{5}$}$
$\text{= $\dfrac{25}{20}-\dfrac{4}{20}$}$
$\text{= $\dfrac{21}{20}$}$