b, $\frac{2x}{5}$ = $\frac{4y}{3}$ =$\frac{3z}{10}$ ⇒$\frac{2x}{5.12}$ = $\frac{4y}{3.12}$ =$\frac{3z}{10.12}$

⇒$\frac{2x}{60}$ = $\frac{4y}{36}$ =$\frac{3z}{120}$ 

⇒$\frac{x}{30}$ =$\frac{y}{9}$ =$\frac{z}{40}$ =$\frac{x+y+z}{30+9+40}$ =$\frac{39,5}{79}$ =$\frac{1}{2}$ 

⇒x=15

   y=$\frac{9}{2}$ 

   z= 20

g,$\frac{x}{2}$ =$\frac{y}{3}$⇒$\frac{x}{10}$ =$\frac{y}{15}$ 

  $\frac{z}{4}$ =$\frac{y}{5}$ ⇒$\frac{z}{12}$ =$\frac{y}{15}$ 

⇒$\frac{x}{10}$ =$\frac{y}{15}$= $\frac{z}{12}$= $\frac{x+y-z}{10+15-12}$ =$\frac{-39}{13}$ =-3

⇒x=-30

   y=-45

   z=-36

i, 2x=3y⇒$\frac{x}{3}$ =$\frac{y}{2}$ ⇒$\frac{x}{21}$ =$\frac{y}{14}$ 

  5y=7z⇒$\frac{y}{7}$ =$\frac{z}{5}$ ⇒$\frac{y}{14}$ =$\frac{z}{10}$

⇒$\frac{x}{21}$ =$\frac{y}{14}$ =$\frac{z}{10}$=$\frac{3x}{63}$ =$\frac{7y}{98}$ =$\frac{5z}{50}$ =$\frac{3x-7y+5z}{63-98+50}$ =$\frac{30}{15}$ =2

⇒x=42

   y=28

   z=20