1. The problem is to find the sum of 8 and 4. 2. The formula for addition is $a + b = c$, where $a$ and $b$ are numbers to add, and $c$ is the result. 3. Substitute the values: $8 + 4$. 4. Calculate the sum: $$8 + 4 = 12$$. 5. Therefore, the total cost for 4 letters is 12 dollars. This matches the pattern in the table where the total cost is $8 + \text{number of letters}$.