(a) The ratio of starfish to sea horses is given as 7 starfish for every 5 sea horses. This can be written as:
\[ \text{Ratio of starfish to sea horses} = 7:5 \]
(b) If we denote the number of sea horses as \( x \), we know that the ratio of starfish to sea horses is maintained at 7:5. This means that for every 5 sea horses, there are 7 starfish.
To find the number of starfish when there are \( x \) sea horses, we can set up a proportion based on the ratio:
\[ \frac{\text{Starfish}}{\text{Sea Horses}} = \frac{7}{5} \]
Let \( s \) be the number of starfish. Then we can write the equation:
\[ \frac{s}{x} = \frac{7}{5} \]
To solve for \( s \), we can cross-multiply:
\[ 5s = 7x \]
Now, solving for \( s \):
\[ s = \frac{7x}{5} \]
Thus, the number of starfish in terms of the number of sea horses \( x \) is \( \frac{7x}{5} \).