a. $\dfrac{7}{9}$ + $\dfrac{4}{5}$ + $\dfrac{11}{9}$ + $\dfrac{6}{5}$
= ( $\dfrac{7}{9}$ + $\dfrac{11}{9}$ )+( $\dfrac{4}{5}$ + $\dfrac{6}{5}$ )
= $\dfrac{18}{9}$ + $\dfrac{10}{5}$
= 2 + 2
= 4
b. $\dfrac{21}{36}$ × $\dfrac{39}{14}$ × $\dfrac{54}{13}$
= 27
