To find the scale factor between the two circles, we can use the ratio of their circumferences.
Given:
- Circumference of circle \( X \) = 120 centimeters
- Circumference of circle \( X' \) = 90 centimeters
The scale factor \( k \) can be calculated using the formula:
\[ k = \frac{\text{Circumference of } X'}{\text{Circumference of } X} \]
Substituting the values:
\[ k = \frac{90}{120} \]
Now, we can simplify the fraction:
\[ k = \frac{90 \div 30}{120 \div 30} = \frac{3}{4} \]
So, the scale factor is \( \frac{3}{4} \).