Given that triangles \( \triangle XYZ \sim \triangle AYB \), we can use the properties of similar triangles to establish a relationship between their corresponding sides.
We are given the following dimensions:
- \( XY = 24 \) yards
- \( YZ = 30 \) yards
- \( YA = 8 \) yards
Let \( YB \) be the length we need to find. According to the property of similar triangles, the ratios of corresponding sides are equal. Therefore, we can write:
\[ \frac{XY}{YA} = \frac{YZ}{YB} \]
Substituting in the known values:
\[ \frac{24}{8} = \frac{30}{YB} \]
Now simplify \( \frac{24}{8} \):
\[ 3 = \frac{30}{YB} \]
Cross-multiply to solve for \( YB \):
\[ 3 \cdot YB = 30 \]
Now, divide both sides by 3:
\[ YB = \frac{30}{3} = 10 \text{ yards} \]
Thus, the length of \( YB \) is \( \boxed{10} \) yards.