1. **State the problem:** Calculate the value of $\frac{21}{3} - \frac{25}{6}$. 2. **Find a common denominator:** The denominators are 3 and 6. The least common denominator (LCD) is 6. 3. **Rewrite each fraction with the LCD:** $$\frac{21}{3} = \frac{21 \times 2}{3 \times 2} = \frac{42}{6}$$ $$\frac{25}{6} = \frac{25}{6}$$ 4. **Subtract the fractions:** $$\frac{42}{6} - \frac{25}{6} = \frac{42 - 25}{6} = \frac{17}{6}$$ 5. **Final answer:** $$\frac{17}{6}$$ This is an improper fraction and can also be written as a mixed number: $$2 \frac{5}{6}$$