Answer:
13 cm
Explanation:
The good news is that you don't need a ruler!
First, you see that the eraser is approximately 5 cm in length, so you must your mind to mentally picture the eraser beside it. You end up with 10 cm. Then, you see that there is more space left on the stick. You know that another complete eraser will not fill up that space. So, you must ask yourself: What is larger than 9 cm, but smaller than 15 cm? The answer is 13 cm!