To find the actual diameter of the button, we can use the fact that the image is 6 times the actual size of the button.
Given:
- Diameter of the image = 21 cm
- Magnification = 6 (The image is 6 times larger than the actual size)
We can find the actual diameter of the button (let's call it \( d \)) using the formula:
\[ \text{Diameter of the image} = \text{Magnification} \times \text{Actual diameter} \]
So, we have:
\[ 21 , \text{cm} = 6 \times d \]
Now, solve for \( d \):
\[ d = \frac{21 , \text{cm}}{6} = 3.5 , \text{cm} \]
Thus, the actual diameter of the button is 3.5 cm.