We first determine the length of the side of the triangle on the left, that is:
![s=\sqrt[]{20^2-12^2}\Rightarrow s=16](https://img.qammunity.org/2023/formulas/mathematics/college/s0v644w7l3387av5zc9jfe7kfqh9pja82i.png)
Now, we can see that 24 = s + a, where s is the side we just determined and a is the side of the smaller triangle in the right, now we replace and solve for a:

Now, we determine the missing side of the whole triangle:
![s_1=\sqrt[]{12^2+8^2}\Rightarrow s_1=4\sqrt[]{13}](https://img.qammunity.org/2023/formulas/mathematics/college/vjjyq6ltgnm4h4fy6qk7jz2wzyk2ox5h62.png)