To find out how many turtles there are when there are 18 sea lions, we can set up a proportion based on the ratio of turtles to sea lions.
The ratio given is 5 turtles for every 6 sea lions. This can be expressed as:
\[ \frac{\text{Turtles}}{\text{Sea Lions}} = \frac{5}{6} \]
Let \( T \) be the number of turtles. When there are 18 sea lions, we can set up the equation:
\[ \frac{T}{18} = \frac{5}{6} \]
To solve for \( T \), we cross-multiply:
\[ 6T = 5 \times 18 \] \[ 6T = 90 \]
Now, divide both sides by 6 to find \( T \):
\[ T = \frac{90}{6} = 15 \]
So, if there are 18 sea lions, there are 15 turtles.