Frazione

(10/9x3/5-1/6-1/8):(3/4-2/3)x2/9+(2-1/7:4/21) =

= (2/3-1/6-1/8):(1/12)x2/9+( 2- 3/4) =

= (3/8):(1/12) x 2/9 + (8-3)/4 = 

= 9/2 x 2/9 + 5/4 =

= 1 + 5/4 = 9/4

(10/9×3/5-1/6-1/8) : (3/4-2/3)×2/9+(2-1/7:4/21)

========================================================

$\small \left(\dfrac{10}{9}·\dfrac{3}{5}-\dfrac{1}{6}-\dfrac{1}{8}\right) : \left(\dfrac{3}{4}-\dfrac{2}{3}\right)·\dfrac{2}{9}+\left(2-\dfrac{1}{7} : \dfrac{4}{21}\right)=$

$\small = \left(\dfrac{\cancel{10}^2}{\cancel9_3}·\dfrac{\cancel3^1}{\cancel5_1}-\dfrac{1}{6}-\dfrac{1}{8}\right) : \left(\dfrac{9-8}{12}\right)·\dfrac{2}{9}+\left(2-\dfrac{1}{\cancel7_1}·\dfrac{\cancel{21}^3}{4}\right)=$

$\small = \left(\dfrac{2}{3}·\dfrac{1}{1}-\dfrac{1}{6}-\dfrac{1}{8}\right) : \dfrac{1}{12}·\dfrac{2}{9}+\left(2-\dfrac{1}{1}·\dfrac{3}{4}\right)=$

$\small = \left(\dfrac{2}{3}-\dfrac{1}{6}-\dfrac{1}{8}\right)·\dfrac{12}{1}·\dfrac{2}{9}+\left(2-\dfrac{3}{4}\right)=$

$\small = \left(\dfrac{16-4-3}{24}\right)·\dfrac{\cancel{12}^4}{1}·\dfrac{2}{\cancel9_3}+\left(\dfrac{8-3}{4}\right)=$

$\small = \dfrac{\cancel9^3}{\cancel{24}_8}·\dfrac{4}{1}·\dfrac{2}{3}+\dfrac{5}{4}=$

$\small = \dfrac{3}{8}·\dfrac{8}{3}+\dfrac{5}{4}=$

$\small = \dfrac{\cancel3^1}{\cancel8_1}·\dfrac{\cancel8^1}{\cancel3_1}+\dfrac{5}{4}=$

$\small = 1+\dfrac{5}{4}=$

$\small = \dfrac{4+5}{4}=$

$\small = \dfrac{9}{4}$