1. **State the problem:** Simplify the expression $$\frac{4}{b} - \frac{1}{a}$$. 2. **Recall the formula for subtraction of fractions:** To subtract fractions, find a common denominator and then subtract the numerators. 3. **Find the common denominator:** The denominators are $b$ and $a$, so the common denominator is $ab$. 4. **Rewrite each fraction with the common denominator:** $$\frac{4}{b} = \frac{4a}{ab}$$ $$\frac{1}{a} = \frac{b}{ab}$$ 5. **Subtract the fractions:** $$\frac{4a}{ab} - \frac{b}{ab} = \frac{4a - b}{ab}$$ 6. **Final answer:** $$\boxed{\frac{4a - b}{ab}}$$ This is the simplified form of the expression.