1. **Stating the problem:** We need to find the original number when given a percentage of it. 2. **Formula used:** If $p\%$ of a number $N$ is given as $V$, then $$\frac{p}{100} \times N = V$$ To find $N$, rearrange: $$N = \frac{V}{\frac{p}{100}} = \frac{V \times 100}{p}$$ 3. **For part (a):** Given 72% of the number is 58. $$N = \frac{58 \times 100}{72}$$ Calculate: $$N = \frac{5800}{72}$$ Simplify by canceling common factors: $$N = \frac{\cancel{5800}}{\cancel{72}} = 80.555... \approx 80.5$$ 4. **For part (b):** Given 11% of the number is 42. $$N = \frac{42 \times 100}{11}$$ Calculate: $$N = \frac{4200}{11}$$ Simplify: $$N = 381.8181... \approx 381.81$$ 5. **Explanation of your thinking:** You correctly used the formula to find the original number by dividing the given value by the percentage expressed as a decimal. This means you took the part (like 58 or 42) and divided it by the fraction of the percentage (72% or 11%) to find the whole number. This is a standard approach to reverse percentage problems and your answers are accurate approximations.