Answer:
~ 30 centimeters of the fish in the poster ~
Explanation:
Let us plan out our steps, and solve for each:
1. Given the information, let us create a proportionality as such:
3 = 1 ⇒ x - centimeters of the fish in the poster
x 10
2. Now let us cross multiply, and solve through simple algebra for x:
3 * 10 = x,
x = 30 centimeters of the fish in the poster