1. **State the problem:** We need to find the average revenue of a shop over four months with revenues ₵18,500, ₵20,000, ₵21,500, and ₵24,000. 2. **Formula for average:** The average (mean) of $n$ numbers $x_1, x_2, ..., x_n$ is given by: $$\text{Average} = \frac{x_1 + x_2 + \cdots + x_n}{n}$$ 3. **Apply the formula:** Here, $n=4$ and the revenues are $18500, 20000, 21500, 24000$. 4. **Calculate the sum:** $$18500 + 20000 + 21500 + 24000 = 84000$$ 5. **Calculate the average:** $$\frac{84000}{4} = 21000$$ 6. **Interpretation:** The average revenue over the four months is 21000. **Final answer:** The average revenue is 21000.