1. **State the problem:** Shelby's Cafe sold 80 espressos in total, and 20% of them were single-shot. We need to find how many single-shot espressos were sold. 2. **Formula used:** To find a percentage of a number, use the formula: $$\text{Part} = \text{Percentage} \times \text{Total}$$ where Percentage is expressed as a decimal. 3. **Convert percentage to decimal:** 20% = $\frac{20}{100} = 0.20$ 4. **Calculate the number of single-shot espressos:** $$\text{Single-shot} = 0.20 \times 80 = 16$$ 5. **Answer:** The cafe sold **16 single-shot espressos** yesterday afternoon.