Horna had a string that was 86 cm long. We need to find the length of the string in millimeters.

Here's the solution to Question 3:

Question 3:
Horna had a string that was $86 \text{ cm}$ long. We need to find the length of the string in millimeters.

Step 1: Convert the length from centimeters to millimeters. We know that $1 \text{ cm} = 10 \text{ mm}$.

$$86 \text{ cm} = 86 \times 10 \text{ mm} = 860 \text{ mm}$$

The length of the string is $\text{860 mm}$.