We are given the following proportions:
![\begin{gathered} x:y=3:9 \\ y:z=6:20 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/nfvukkub0a71kbimokrfj6pgpcfw56mknm.png)
The second proportion is equivalent to:
![(y)/(z)=(6)/(20)](https://img.qammunity.org/2023/formulas/mathematics/college/8lbr6mp5qhv6l0osraq99xvnc435s4hd50.png)
Now, we substitute the value of "z":
![(y)/(30)=(6)/(20)](https://img.qammunity.org/2023/formulas/mathematics/college/g3ob8bwcb7zc46n1tmajw7p328g3jwelds.png)
Now, we multiply both sides by 30:
![y=30*(6)/(20)](https://img.qammunity.org/2023/formulas/mathematics/college/x8ziv6d691hpdsqavkz6klqlco1jmt37vi.png)
Solving the operation we get:
![y=9](https://img.qammunity.org/2023/formulas/mathematics/college/n25el6v67kley8eimh9h2v92vr4n2cvk5t.png)
Now, since we have the value of "y" we can use the first proportion to get the value of "x":
![x_:y=3:9](https://img.qammunity.org/2023/formulas/mathematics/college/9omqcfd4p2m6r7mo8kv1sv27scg0u5mi5j.png)
This is equivalent to:
![(x)/(y)=(3)/(9)](https://img.qammunity.org/2023/formulas/mathematics/college/5s303nrhcsal6x6n8cor6kcnzt23p0rkym.png)
Now, we substitute the value of "y":
![(x)/(9)=(3)/(9)](https://img.qammunity.org/2023/formulas/mathematics/college/du5vk1eqs5qzyj4mf3pu6vxsalc1fcwwm6.png)
Now, we multiply both sides by 9:
![x=9*(3)/(9)](https://img.qammunity.org/2023/formulas/mathematics/college/7hlemghb5bq5rznu32cs5vr8o0jhyq3vsb.png)
Solving the operations:
![x=3](https://img.qammunity.org/2023/formulas/mathematics/high-school/tu78xmfzid4zbk5fl1tm8vw66ibi0yce1h.png)
Therefore, the value of "x" is 3.