1. **State the problem:** We want to find the percentage $x$ such that 15.5 is $x\%$ of 77.5. 2. **Formula used:** The general formula to find $x\%$ of a number is: $$\text{Part} = \frac{x}{100} \times \text{Whole}$$ Here, Part = 15.5 and Whole = 77.5. 3. **Set up the equation:** $$15.5 = \frac{x}{100} \times 77.5$$ 4. **Solve for $x$:** Multiply both sides by 100 to eliminate the denominator: $$15.5 \times 100 = x \times 77.5$$ 5. **Intermediate step with cancellation:** $$\cancel{15.5} \times 100 = x \times \cancel{77.5}$$ Actually, we divide both sides by 77.5 to isolate $x$: $$x = \frac{15.5 \times 100}{77.5}$$ 6. **Calculate the value:** $$x = \frac{1550}{77.5} = 20$$ 7. **Answer:** 15.5 is 20% of 77.5.